RADIO'S LIVEST MAGAZINE...500 S. Paulina St., Dept.92.8H Chicago, Ill. Dear Mr. Lewis: Send me your Big. FREE Radio Book. and tell me how f can get the TRAINING that will make me a

r.

RADIO'S LIVEST MAGAZINE December 25 Cent-7;

HUGO GERNSBACK Edo,

How to Make a

Battery-Operated,

Portable P. A. System See Page 330

A ,

A Direct-Reading Mutual Conductance Meter-A 2-Volt Super. Remote-Control Tuning System - Noise Meters - I. F. Chart

www.americanradiohistory.com


SPEED SPEED SPEED

WHEN EFFICIENCY IS DEFINITELY LINKED WITH SKILL OF

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JOINED WITH PROGRESSIVE RESEARCH

THEN ONLY IS THE RADIO PUBLIC EQUITABLY SERVED

SPE E D POLICIES ASSURE THIS ALWAYS

TRIPLE-TWIN- TELEVISION -FOTO- LECTRIC

TUBES WRITE FOR LATEST FREE BULLETIN -TURN TO PAGE 384A FOR OUR CARD -KEEP UP WITH PROGRESS BY CONTACT WITH

CABLE RADIO TUBE CORP. 230 -240 NO. NINTH ST. BROOKLYN, N.Y.



4-;4.;

ARE YOU

'SET" TO START THE RACE TO

BETTER TIMES

LEARN

CYIA° MAN

MM .1411"

./ It's just as true -or even truer -in business as in sport. The man with real, practical TRAINING is the one to win. Now that business is returning to normal there's going to be a harder race to win the prizes of big -pay jobs, independence and a future, than ever before. Are you "all set" to race? Have you the necessary TRAINING to bring you in among the winners! If not, DON'T WAIT! Get the training NOW while there's still time!

Get Your Training for Work in Profitable

RADIO-TELEVISION in the Great Coyne School in only I O Weeks Here's the most fascinating. fastest -growing field in the ing Picture and Television and Sound Work! In just a world today. In Radio there are thousands of jobs pay- few short weeks, by exclusive Coyne methods, you are ing BIG MONEY -up to $50 a week and more. COYNE trained for a future that holds marvelous opportunities TRAINING fits you to hold better jobs -prepare to be for top -notch salaries, or for a business of your own a Designer, Inspector or Tester ... a Radio Salesman. and real independence. Find out about this great game - Service or Installation Man . .. Operator or Manager get all particulars -see how simple it is for any ambi- of a Broadcasting Station ... a Wireless Operator on tious man to get into it with the help of this great, ns- a Ship or Airplane ... Coyne trains you. too, for Talk- tionally- recognized school.

BY DOING -NO BOOK STUDY When you come to COYNE for training you start right in doing practical,interestingwork on the greatest layout of Radio, Television and Sound Equipment you ever dreamed of seeing. Scores of the most up -to- minute Radio Receivers, real Broadcasting Equipment, latest Television Apparatus, Talking Picture and Sound Re- production Equipment, Code Practice Equipment, etc., are here for you to use and learn by actual operation, servicing and repair. Previous experience or advanced education isn't needed. The useless theory -the tedious book study -is cut out by COYNE methods. We replace it with actual practice and experience in modern, completely equipped shops in our own huge building. The result is that you get more training in 10 weeks at COYNE than you ordinarily could in long months of tiresome book study.

Earn as You Learn - We'll Help You Don't let lack of ready cash hold you back in getting the TRAINING you must have to be a winner. Many COYNE students make all or a good share of their living expenses while going to school. If you need that kind of help just let me know. We run an efficient Employment Service to help you get spare -time employment while you are here -and that aids you in finding full -time jobs whenever you need them during yr..r whole life. COYNE has been training men for nearly a THIRD C_ A CENTURY -its value has been tested and proven by thousands of men who are now successful and happy. YOU can have a future like that -YOU can be one of the winners in the race of life. Why not learn how easy it is

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RADIO -CRAFT for DECEMBER, 1932

COYN 500 S. Paulina St.,

ELECTRICAL SCHOOL E H. C. LEWIS, President Founded 1899

Dept. 92 -8H CHICAGO, ILL.

iI. C. Lewis. President, Radio Division, Coyne Electrical School. 500 S. Paulina St., Dept.92.8H Chicago, Ill. Dear Mr. Lewis: Send me your Big. FREE Radio Book. and tell me how f can get the TRAINING that will make me a WINNER.

ADDRESS. CITY__.._..........__...... .._..._..._..- ._....._._...._ ._...._..STATE. ._..._...._._..._

321



(Rdio.aft\ FOR THE

SERVICE MAN. DEALER . RADIOTRICIAN

HUGO GERNSBACK, Editor -in -Chief LOUIS MARTIN R. D. WASHBURNE Associate Editor Technical Editor

CONTENTS OF THE DECEMBER, 1932, ISSUE

VOLUME IV NUMBER 6

EDITORIAL:

What Broadcasting Needs Hugo Gernsback

NEW DEVELOPMENTS IN RADIO:

329

How to Make a Battery- Operated, Portable P. A. System

Clifford E. Denton 330

The Latest Radio Equipment 332

New Tube Announcements Louis Martin 334

SERVICE MEN'S DEPARTMENT:

Building A Direct- Reading Mutual Conductance Meter J. H. Potts 341

The Causes and Cures of Audio Oscillation L. van der Mel 343

RADIO-CRAFTS Chart of Intermediate Frequencies 344

Constructing Adapters for Test Equipment F. L. Sprayberry 346

The Service Man's Forum 348

Operating Notes 349

RADIO SERVICE DATA SHEETS:

Bosch "Vibro- Power" Triple Action Model 312 350

Sparton "Triolian" 13 -Tube Model 28 351

Short-Cuts in Radio Service ... 352

A Service Man's Proportional -Type Ohmmeter Frank Zoltowski 384A

TECHNICAL RADIO TOPICS:

Building A Remote Control Tuning System C. H. West How to Build the Savil Type 748 D. C. Kit Set

B. S. Vilkomerson

Constructing A 2 -Volt Superheterodyne H. G. Cisin

Some Interesting Loudspeaker Facts Eli M. Lurie

"Ferrocart" R. F. Coils Albert Neuberger

How to Make Money With P. A. Systems Hubert L. Short

IN OUR NEXT FEW ISSUES: A METERLESS TUBE TESTER. Since time immemorial it has been

considered essential that one or more meters be included in

the construction of a tube checker. In the "meterless" tube checker the author presents an instrument capable of testing practically all tubes -without recourse to any type of meter.

SET TESTING BY RESISTANCE MEASUREMENT. In this article the Service Man will find a practical discussion of the procedure to be followed in "resistance servicing." After a short discussion of the principles involved, the author conducts his readers through a series of tests on a standard, commercial, receiver chassis.

NEW TUBES -AND CIRCUITS. Interesting as have been previous articles in RADIO -CRAFT, on the design and use of new types of tubes, still newer designs present additional features to whet the interest of technicians. Not to know the features of these new electronic devices is to be "out in the cold" as regards progress of radio equipment development.

RADIO -CRAFT is published monthly, on the fifth of the month preceding that of date; its subscription price is $2.50 per year. (In Canada and foreign countries, $3.00 a year to cover additional postage.) Entered at the post office at Mt. Morris, Ill., as second -class matter under the act of March 3, 1879. Trademark and copyright by permission of Gernsback Publications, Inc., 98 Park Place, N. Y. C. Text and illustrations of this magazine are copyright and must not be reproduced without permission of the copyright owners. We are also agents for WONDER STORIES and WONDER STORIES QUARTERLY. Subscription to these magazines may be taken in combination with RADIO -CRAFT at reduced Club rates. Write for information.

Copyright 1932. GERNSBACK PUBLICATIONS, INC.

HUGO GERNSBACK, President J. M. HERZBERG, Vice -President S. GERNSBACK, Treasurer I. S. MANHEIMER, Secretary

336 Published by TECHNI -CRAFT PUBLISHING CORPORATION. Pub- lication office: 404 N. Wesley Ave., Mount Morris, Illinois. Editorial and Advertising Office: 96 -98 Park Place, New York City. Chicago Advertising Office: 737 North Michigan Avenue, Chicago, Ill. Western Advertising Office: 220 No. Catalina St., Los Angeles, Calif. L. F. McClure, Chicago Advertising Representative. Loyd B. Chappell, Western Advertising Representative.

338

340

342

345

353

RADIO -CRAFT Kinks 354

The Radio Craftman's Page 355

Constructing the Triple -Twin S.-W. Receiver H. Harrison 356

Information Bureau 358

Quasi -Optical Home Experiments John B. Brennan, Jr. 360

Book Review _. 361

How to Get "Java" on a P. A. System ..Paul Richards 3848

322

London Agent: Hachette :i Cie., 3 La

Paris Agent: Hachette & Cie., III Rue Reaumur

Belle Sauvage, Ludgate Hill, E.C. 4 Australian Agent: McGill's Agency

179 Elizabeth St., Melbourne



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Ii. ii. SCOTT RADIO LABORATORIES, INC.

44W Ravetuwood Ave., Dept. C -122 Chicago, Illinois

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324

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DECEMBER, 1932



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,list/ /Last Minute Adapter Equipment, .Xeres what you have been looking for/

950XYL

Forty in One

Adapter Change

Here's what you have been looking for -nothing like it -highgrade tube checking adapter -tests over 40 tubes. No leads -no jacks or plug -no complicated directions. Resistances and toggle switch for instant reading of both plates of dual plate tubes- beautiful- ly and ruggedly made -a typical Na -ald product. List $6.00. Servicemen's postpaid price $3.75. Orders filled in sequence received. Do not delay -send order today. Tubes it will check in practically any checker are 19. 29, 33. 36. 37. 38. 39. 41, .12, 44, 46, 47, 49, 52. 55, 57, 58, 59. 64, 65, 67. 68, 69, 70, 80, 82, 83. 85. 88. 89, 93. 95. 985, 986, G -2, G -4. LA, l'A, PZ, PZH. Wunderlich A and B. No. 950XYL, Servicemen's

price $3.75 postpaid. For Those Who Want In- dividual Tube Checking Adapters Here Are Some

of the Newest 975KP testa the seven prong tubes in the 27

97Sa checker socket. 975K1' List Price $1.00

965KS tests the 57 and 58 in the 21 checker socket and the 89 in the :tt; socket. 965KS Lit Price $1.00

982 tests the 82, 83. 88. 985 and 986 m.v. rectifiers -has protective resistance and toggle switch for testing both plates. 982 List Price $3.00

955G -2 tests the C2. C4, G2 and G4 du "- diode tubes -has protective resistance network and toggle switch for testing each plate. 955G -2 List Price $3.00

965 -55 tests the 5:, in 24 and the 85 in 36 checker socket. Both triode and diodes are tested Has protective resistance network. 965 -55 List Prise

$3.00

965 -55 965CG testa 57, 5' and PZH in 24 socket and 41, 42, 89, and PA in 36

checker socket. 965CG List Price $1.25

954KPC tests 33. 49: 46. 47. PZ; 52, LA in 30; 45; TIA checker sockets. 954KPC List Price $1.00

Send stamp for chart showing adapters best suited for the instruments you have. Chart includes adapters for all makes of instruments and all types of tubes.

965 CO

9/11

INSIDE FACTS Testing Seven Prong Tubes tlt,nn the advent f eia -pinne tunes. instru-

ment roder shifted almost immediate', g'pron` analyser phw..

Now nced

that is the g...?Inn wheth. there is ie to h. a seven -prong analyser plue waste/

nt We hove designed ouch plug to have ern writ timers

nhrone a.ken I re,, mettI. dom.

Plant with n roll gri

weevers-prong e..,p.

w

In the ho very definite dinadyan es in 'having s .esen roes nely.ar plug.

It .. would

mean that at

almost invariably used

máh the

adapter. Thu added length would si ° he a disadvantage i slowly shielded tee and others built in limited wasp. r

In addition with

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er ere m which tore in a mho- Id having Underwriters 1-32 in. clearance between' it and the tune

bsTn meet these condition. anslywr plug. made

In with theenet era of he wet

te úil:°pmtnen wt, ..: d the ° adaptrn will not

g then th e stallnt tube have

ase of given number

to the e& Men ofeNa -aid Adapters.sa been given

knowledge w.ofare t lead' wt instrument combined

cotrute and both weevil Tube

fu ure ï rei.ní ;(i-

Ades.taken o co-nod/nation. Th

Nteril correct. ce dpendable .

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n.roueadapers are built with current limiting Where tubes have more than

element wmmn checking they are resided with toggle.vitebes that loth plates or sections of such 'bee m e

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Here Are the New Analy- zer Plugs and Adapters for the New 6 and 7 Prong

Tubes The 906WT. is the last

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96596

967 SS

906W L List Price... $3.50

906WLC Above with five feet of seven wire cable with the seventh w

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96405 6 hole to 4 prong adapter with locking stud

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965DS 6 hole to 5 prong adapter with locking tud

$1.25 967SS 6 hole to 7 prong adapter with locking stud connected to control-grid prong $1.25

'r ?. 967SGL 6 hole to 7 prong adapter with locking stud. l'on trol -grid prang eon- fleeted to lead with clip for attaching to control-grid

967466 stud on analyzer plug. $1.50

Keadrite Owners If you have endeavored to

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Change your equipment over to the Alden Analyzer Plug and Na -ald Adapters and avoid being disap- pointed.

Revamp the Old Set An- alyzer and Tube Checker or Build a New One Using the New Na -Ald Latch - Lock Analyzer Plug and

Universal Sockets Revamp the old set analyzer and tube checker or build a new one with the new Na -ald Latch Lock Analyzer Plugs and Universal Sockets. See articles on new analyzers by Denton and Sprayberry in Radio Craft. Clain, Gerber. Shalleross and Van Leuven in Radio News and Bernard In Radio World. Watch tor coming articles using Naald Plugs and Uni- versal Sockets.

456 Four. five and six hob, composite sock - ts SOc

456E Four. five and eis hole c MIpost«. sort - 437 Seven b le 4socket

to match 56 35e

1 437E Seven hole socket p,

41W 431e match 456F 40e 456 and 437 are

used in new equipment or to provide nix and s prong sockets without adding additional socket holes to present equip -

rnt. 456E and 437E are a Rise of socket found i n stone of the older test equipment.

These are the fine brilliantly colored to- cat er-ring sockets P pouring in ome of the newest sad most ml-

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965 -50

964 -4r

419%

Adapters for Us- ing the New Tubes in Your Present

Set 954 -47 replaces 45 tubes with 46 or 47 pentodes 50c 965 -58 replaces 24 tubes with 57 or places the 58 in a 35 or 51 socket 50e 927 replaces Kellogg overhead heater type tubes with the 27 $1.25 419X places the 2 volt tubes in old UV sockets 35c 999 places any UX- base tube in a UV199 socket 75c

Servicemen's discount 35'; -if order amounts to $6.00, discount is 40';, -Send for catalog.

Here Are Adapters 'l'hat Make it Possible to Use the UY Plug of Your An- alyzer for 6 and 7 Prong

Tubes Here are twin adapters which make it possible to use older analyzers for pentodes, 6 and 7 pin tubes. 974 Analyzes

9659W pentode circuits with screen grid analyzers. 974 List price $2.50 965DW analyzes 6 prong tube circuit with screen grid an-

alyzers. 965DW List price $2.50

975DW analyzes 7 prong tube circuits with screen grid analyzers. 975DW List price $2.50 If central locking stud to fit Na -ald Latch Lock plug is desired add "S" to any above numbers.

The genuine Maka- lot Coil Forms with color - code ring. Red -

yellow- blue -green. List price 4 and 5 prongs 25c each 6 prongs 30e each

103 Precision wound shortwave coils -20 to 200 meters with .00014 mfd. condenser. 704SWS Set of four coils

$2.00 Precision wound broadcast coils 100 -540 meters with .00014 mfd. condenser 704SWW 704SWO Set of two coils `1. -to

Practice Code Set. Adjust- able pitch buzzer. Makalot base with code molded in. Alden Code Set. List price

75e

Send 10c for 26 page data sheets - 300 diagrams of adapters for every purpose -description, use and directions are given. Tube terminals of the new tubes are shown, adapters for pickups. microphones, output meter, .

tone control, shortwave con verters. etc

Alden Mfg. Co., Dept. R, 115 Center St., Brockton, Mass IVA-AUD

326 RADIO -CRAFT for DECEMBER, 1932



The Seasons ßiß Radio Sensation.

Bte: ALL-WAVE

Completely

Assembled

with Large

DUAL AKERS

_ All the New 1933 FEATURES

WHAT a radio! One complete 16- tube chassis with one dual -ratio dial -new Super -Heterodyne

circuit with a range of 15 to 550 meters .... STAT -OMIT Tuning Silencer New Class "B" Push -Push Power Amplifier . Color -Lite Tuning .. . Full band automatic Volume Control .... Duplex Duo -Diode Detection

Dual -Ratio Single D ial . No Trimmers, No Plug -in Coils, No Tuning meter or Neon light required

Fractional Microvolt S ensitivity . . . Dual Pow- ered (2 separate power Transform- ers) . . . Absolute Tone Fidelity .

18 Tuned Circuits . . New Mercury Rec- tifier Full- Floating Variable Condenser

Low Operating Cost . . . and many other sensational new features. The new Midwest 16 -tube set actually uses less current than previous sets of 8 and 10 tubes. A bigger, better, more powerful, more selective, finer toned radio than you've ever seen before . offered at an amazingly low price direct from the big Midwest factory. Mail the coupon or send name and address on a postal for catalog and complete details.

30 AY5 FREE TRIAL

e.tts: .i,,,ttmfiii:z,:

Remember! DEAL DIRECT WITH FACTORY! Every Midwest set is backed Don't be satisfied with less than a Midwest 16 -tube A. by a positive guarantee of C. radio. A receiver covering only the regular broad- satisfaction or your money cast waves is only half a set. Improvements in short- SAVE back. 30 DAYS FREE wave programs have made ordinary broadcast sets TRIAL in your own home

P gr Y UP TO makes you the sole judge. obsolete. The Midwest gives you regular, foreign, po- Midwest, now in its twelfh lice and amateur broadcasts in one single dial set. No successful year, offers big - converter or any extra units required. 50% gar, better, more powerful, Remember, you buy DIRECT FROM THE MAKERS. more sensitive radios at low - No middlemen's profits to pay. You get an absolute er prices than ever before. guarantee of satisfaction or money back. You try TERMS br n scoupon

or a postal any Midwest 30 DAYS before you decide to keep it. a you big new catalog Then, if you wish, you can pay in small monthly caLoroa, and complete in- Then, formation. Mail it amounts that you'll scarcely miss. Mail coupon for full QQ

details or write us a postal. $DS OO NOW! 0ß Read These

west Letters From Mid- s°pti i4,0°

S E1p cs Just two of the thousands of letters praising Midwest Radios. N V t GlfoaveF received f Spain. Italy, ,I °am

Ach satisfied In every oils vtF r XTAMo ó

stations such us FYA, France: F,AQ, way with my Midwest radio. 1 heard ß 1 0E ` ' 0 Madrid. Spain; 12 RO, Rome, Italy; Sydney. Sunday 3:00 A. M. Also M , U xbet,. and last but not least JIAA, Tokyo, %YMXN. W3XAL, WIXAZ, W2X:AF,

Complete Line of Japan. I really think the Midwest in the evening. On the regular band NO COty tot set is a miracle." have some 55 stations so far."

. aSVG New Consoles A. F. GRIDLEY, Aug. llalbl, 1427 Myra Ave..

The big new Midwest catalog shows Sarasota, Fla. Los Angeles, Calif. tapegs b0 Va <t seÑ gorgeous line of artistic consoles in Investigate! Mail Coupon NOW! tN O s 'o- v a

the new

nowi. 10g Get sl

all the Mail

faclee Get the Midwest catalog. Learn the facts about Midwest 9. 12 and 16-tube aea98QOj.0..-,,,,o00'..,

eat °bet &s nor Mt'

Learn how you can save r to ALL -WAVE sets. a Learn about our sensationally low factory prices, easy pay- .e 1 5 v try >

50% on a big powerful radio by any tradic until positive

get °thee big new Midwest ncatalog. Jut sign ands mail VO\tbow epa of .t is

ass

o oQat '.-, ordering direct from the factory. the coupon or =end nano and ddrese on pastas. , - - , -

MIDWEST RADIO CORPORATION :t`°°,me - - - ---- ' DEPT. 157 (Est. 1920) CINCINNATI, 01110 ' f.00( ̀ ' Tow °`" so"

RADIO -CRAFT for DECEMBER, 1932 327



Tho first of a series of advertisements devoted to companies out - standing for their engineering efforts and recognized as leaders in their respective field -Number One -TOBE -Radio Noise Suppression.

FILTERIZERS lick your worst enemy

MAN -MADE STAT1C

The TOBE FILTERIZER KIT, as shown above, and easily installed

STOPS ALL RADIO NOISES

ON THE AERIAL

Filterette RF -1 connects antenna with shielded lead -in wire.

ON THE SET Line Filterette RF -2 pre

vents noises from entering set by way of the power line.

TOBE FILTERIZER enables the listener to enjoy noise free radio reception. It keeps out of the set "man-made" static, resulting from motors, flashing signs, and other electrical apparatus. It has been tested by us on all makes of radio and under all conditions and has demonstrated its value.

You can easily install the TOBE FILTERIZER kit which includes:

1 Antenna Unit -RF -1

1 Line Filterette -RF -2

75 Ft. of Filterized Shielded Lead -in

Complete, Ready to Install, $9.75

DISTRIBUTORS IN

RADIO PARTS ONLY

328

_s EWhen you buy a TOBE product to stop

radio noise you obtain equipment which is the result of years of concentrated engineering effort. Everyone in the radio industry is familiar with what the TOBE people have done -to make radio reception better. The position of FIRST is conceded by all, and no finer tribute has ever been paid any company -than to have its work and products endorsed and recommended by the most promi- nent radio and electrical manufacturers. Such companies as Atwater Kent, Aud-

x iola, Clarion, Crosley, Philco, RCA Vic- tor, General Electric, Sparks- Withing- ton, Wright DeCosta, Zenith, and others, are included in this list.

We are proud to be one of the distributors for the FILTERIZER. It is sound- ly engineered, and the issue of the bulletins on filterizing principles which are made available to all dealers by the Tobe Deutschmann Corporation is just one of the many reasons why we consider this product so excellent. The FILTER - IZER is not a "gadget." You mast know how to use it and if anyone can tell us HOW and if anyone KNOWS HOW, it is TOBE DEUTSCHMANN.

NEWARK ELECTRIC CO. A;lhing iuf Seatiio" 226 WEST MADISON STREET

CHICAGO. ILLINOIS

e - Your Discount is 40%

Deposit Required with All Orders




adio@ff FOR THE

SERVICE MAN - DEALER RADIOTRICIAN

"Takes the Resistance Out of Radio"

Editorial Offices: 96 -98 Park Place, New York, N. Y. HUGO GERNSBACK, Editor Vol. IV, No. 6, December, 1972

WHAT BROADCASTING NEEDS

An Editorial by HUGO GERNSBACK

THE thoughtful observer of radio broadcasting in the United States must have long since come to the conclusion that our manner of broadcasting leaves much to be desired. In the first place, there is entirely too

much duplication of features between stations. At the present time of writing, there are actually some 650 odd radio broadcast stations in the United States alone, aside from Canada and Mexico, where there are still more stations.

Large as the United States are, there is not room to operate all these stations at the present time and give the service they should give, for obvious reasons. All you have to do is tune in a dozen different stations during any given evening, and it will become apparent that there is a fearful amount of duplication. You will find the same song being plugged by dozens of different stations. You will find the same sort of features duplicated countless times. For instance, you will get jazz in different forms from stations too numerous to mention. You will get crooners from a like amount. You will get instrumental music, organ music, symphonic and other music in vast profusion, all emanating from different stations.

If you are the average listener, you may, for example, be interested in classical music. At the present time, in order to get it, you must twist the knob of your set until such time when you find such music. Often, during a given period, there may not be any classical music, and if you have no printed program before you, which often happens, you are at a loss to know whether there will be any such music on the air that evening or not. Perhaps in a half hour you try again, and likely as not you butt into the midst of a classical program and you are annoyed because you did not know when it started.

If you have a printed program, it is somewhat simpler, but very often the printed program does not give you all the information you want. Then, too, to the great annoy- ance of listeners, American stations have a fond habit of switching programs around. They cancel one program and put on another. If an important political speaker is on the air, as for instance the President or presidential candidates, as we have at this time of the year, then all other programs go by the wayside and so the printed program is not of much use.

A visitor from Mars on an excursion to the United States, after having investigated radio broadcasting for a few eve- nings, would perhaps scratch his head thoughtfully and ask himself if the inhabitants of the earth had all gone out of their minds. Perhaps he could not understand the haphazard working of our stations, and he might ask questions about it, but no sane reply would be forthcoming.

After all, the problem is a simple one if the Radio Com- mission could be prevailed upon to do something about it, and it would not be so very difficult to solve it, either. Disre- garding the key stations of the national broadcasting nets, as well as the stations connected with the networks, we still have left a fearful amount of stations which duplicate many features that are on the networks. Suppose the Radio Commission were to license independent stations, not affiliated with networks, for only one type of program? Suppose,

in a given city, there are six stations of which two are network stations? This would leave four other stations. The Radio Commission would say to these four stations that thereafter station A would be permitted only to broadcast jazz and light music; station B would only broadcast classical music, heavy music, etc.; station C would only have educational talks or educational features, of which there are a great variety; station D would be used for vocal music only. In localities where there are more than six stations, excellent uses could be found for the others.

This would be the ideal arrangement; to give the broadcast listener a service which he does not get now. He would then know in advance, when tuning -in any station, what sort of entertainment or service he could expect from it. If he wanted jazz, he would tune -in a "jazz station "; if he wanted dance music, he would tune -in a station that would give him nothing but dance music. If he wanted educational talks, he would know where to get them, without twiddling the knobs of his set futilely. In other words, we would have a situation where the listener could, at any time, get what he wanted without having to jump over to the set every fifteen minutes and switch to another station.

Of course, I can see where most broadcasters would throw up their hands in horror at such a suggestion because they cannot conceive of one station giving one sort of entertainment to the exclusion of all others. Yet, the plan has its great advantage in that such a station would become expert in its line, and could give real service which it does not and cannot give today. If you listen in to any of the smaller, independent stations today, nine out of ten programs are distinctly mediocre, to put it mildly. We have poor music, poor talks, and poor singers as a rule, and only the chain - affiliated stations, with the exception of a few of the larger independents, give good features. The smaller stations have no chance at all to give a real service to the listener. They have the poorest bands and the poorest singers and entertainers. All this could be changed if each station were only to broadcast one type of program. They would soon learn to do this one thing well.

Nor would their commercial interests fare worse than now. The advertising talks interspersed between the features would remain just the same. The advertiser is interested in coverage; he can get it just as well from an audience listening to an educational talk as from an audience listening to a crooner.

The trouble with the independent and smaller broadcasters today is that they are ill -fitted for the job simply because they do not specialize. If they specialized in one field they would do a lot better, and what is more, they would really serve the public.

If this recommendation were followed, the constant talk about too many stations would not be so serious; and if a station performs a real service, which many do not do today, the Radio Commission would think twice before depriving such stations of their licenses.

I predict that if some such plan is not adopted, the Radio Commission will find it necessary during the next ten years to reduce drastically the number of stations that are on the air.

329



Fig. A Internal view of the system with the front cover, which holds the speaker, removed and placed on

top.

Fig. B

Photograph of the amplifier itself. The cable connects to the batteries housed in the case.

PUBLIC address equipment finds its way into many fields as the stage, pulpit, auditorium; even the front steps of the village post office

(around election time) offer distinct possibilities.

Most systems offered are dependent for their power supply upon electric - light sockets. This is a condition which limits the field of use for such equipment and enables RADIO -CRAFT to present the first constructional article

HOW TO MAKE A

BATTERY -OPERATED, PORTABLE P. A. SYSTEM Complete constructional details of a battery- operated, portable P. A. system that is simple, economical and en-

tirely self- contained

CLIFFORD E. DENTON

on a system which may be set up anywhere, entirely independent of local power -supply conditions.

This outfit is ideal for the speaker or lecturer who makes short visits to small towns; speaking under conditions that would tax his voice, this amplifier can be used as a voice booster and permit voice conservation. If a phonograph is handy, then the pickup can be used to supply music for intermissions or for dancing.

As a calling system for use in offices, this system offers excellent possibilities. Quick -heating tubes and a simple switching combination for turning on the "mike" current at the same time the filament current for the tubes is applied, provides instantaneous service, and current is consumed from the batteries only when in use.

Design Factors

The amplifier proper consists of three stages of amplification, and has many interesting features. For example, the input transformer has windings for high impedance phonograph pickup, single or double -button microphone, and a high impedance winding used to feed the grid of the first tube which is a '32 tube of the screen -grid type.

A high audio gain in the first stage is necessary to raise the volume level

Fig. C

Under chassis view. The diagram of Fig. 2 shows exactly where the individual parts are placed.

330

to a value sufficient to swing the grid of the second stage which works as a voltage amplifier and semi -power stage. The tube used in this second stage is a '33 power pentode. A tube of this type was selected for use because a certain amount of power is needed to drive the output stage and any other tube which could be used would not have the voltage gain required. A high gain is necessary in this stage for several reasons, the most important being that the input, push -pull transformer has a step down ratio and some of the available signal voltage will be lost in the transfer to the grids of the output stage. The output power of the '33 is about 700 milliwatts, and the voltage gain in this circuit is almost 14. In most cases, the type of tube used as a driver for a class B connection must determine the design of the interstage coupling transformer, and because of the high power output of the '33, a transformer was selected with a low turns ratio. This permits less voltage loss in the coupling transformer with sufficient power to drive the output tubes to near their maximum power output.

The output stage has two of the new class B tubes known as the ER- 49. Ratings and characteristics are as follows: Filament voltage, 2.0; filament current, .12 -amp.

YOU SHOULD BUILD THIS P. A. SYSTEM BECAUSE

It may easily be constructed at home by anyone; It is entirely self -contained -no external apparatus; Public Address systems are in demand everywhere; No large outlay of cash is necessary, the total cost of

the device is about twenty -five dollars, complete (without microphone);

You want to make more money in the radio game;

You WILL make more money in radio by building THIS BATTERY -OPERATED, PORTABLE P. A. SYSTEM

RADIO -CRAFT for DECEw1BER, 1932



.t

As a class B amplifier: Plate voltage, 180; grid bias (both grids), 0; plate current (zero signal), 4 ma.; plate current (peak per tube), 50 ma.; optimum load resistance (per tube), 3,000 ohms; optimum load resistance (plate to plate), 12,000 ohms; power output (two tubes), 3.5 watts.

As a class A amplifier: Plate and outer -grid voltage, 135; grid bias (inner grid), .20 volts; plate current, 6.7 ma.; amplification factor, 4.5; plate resistance, 4,000 ohms; mutual conductance, 1,125 micromhos; power output, 170 milliwatts.

Note that the filament consumption of these tubes is low. Two of them consume less current than one of the '33 type output tubes. Power from the "B" supply is drawn in proportion to the signal supplied to the grid of the output stage. Thus, with no signal, the plate current drain of the output stage is 4 ma. ; with a signal applied, the plate current will rise, at times, to 20 ma. But because this drain is not constant, small size "B" batteries can be used and still give satisfactory life.

The output transformer has a center- tapped primary and offers four values of output impedances suitable for matching most any type of speaker. A connection strip on the side of the chassis permits the selection of either 9 -, 15 -, 500- or 4,000 -ohm windings for proper output matching.

Current for the microphone is supplied by tapping off 1.5 volts of the filament supply battery. If a single - button microphone is used, connect leads from the "mike" to input terminals 4 and 5. Double button "mikes" are connected in the conventional manner to terminals 3 and 5 (from the button terminals) and from terminal 4 to the common connection of both buttons.

Volume control is obtained by varying the position of the slider arm of potentiometer 8 of Fig. 1. This is a simple, low -cost method to use, and does not affect the frequency charac teristic of the input audio transformer except at very low volume levels. Practical experience indicates the average setting of this control will be about half -way on.

Terminals 1 and 2 of the input strip are connected to the high impedance winding of the input transformer. This winding is suitable for matching a high impedance phonograph pickup to the grid of the tube. This gives better frequency response and greater gain whenever it is desired to use the amplifier in conjunction with a phonograph.

The construction of the completed system must be divided into two sections: The wooden carrying case; and the chassis of the amplifier, which is made of iron and painted black with a quick -drying enamel.

A detailed drawing covering the construction of the case is shown in Fig. 3 and in Fig. A. If the builder cannot make the box, it is wise to turn the job over to a carpenter so as to

(Continued on page 364)

(1)

(21 (3)

(4)

(3)

(6)

C

( 9 ), (13) 1) 53 (16) 32 (17)

i 49

(12)

f

(A)

(20) (21) (22)

(24)

(25)

(26) 28)

' - GNO.

BLACK, ¡KNOT

"A+"It/2V.

CHASSIS / A GREEN

"C=16.5V.

(27) RED YELLOW

1 BLACK

-c +-

Fig. I

Complete schematic of the amplifier. The reference numbers are used in the List of Parts and in the sketch of Fig. 2.

s M

i

14%4. 81"

23/4 y

%¡

o

tel =

SEND UP

S END D OWN

MAT: - VIII-METAL

sE

a

QI

Q1

SEND UD 4j ND

DOWN

,r/' 4

UNLESS OTHERWISE SPECIFIED ALL HOLES ARE E/32" INA y ̀ BAKELITE TERMINAL STRIPS

Fig. 2

Complete chassis layout of the amplifier. The two terminals labeled P.P connect to phonograph pickup; M and MC to a single -button microphone; M MC, and M to a double -button microphone; and G to ground. Terminals L and 9 connect to a 9-ohm load; terminals L and 15 to a IS -ohm load;

H and SC to a 500 -ohm load; and H and 4M to a 4.000 -ohm load.

II*

-END VIEW- SNOWING FIIONTA AFAR COVER FASTENINGS

t REQUIRED ONE FRONT AND OWE SEAR COVER

Sr

RADIOCRAFT for DECEMBER, 1932

Fio. 3

Details of construction of the boo for the system.

331



THE LATEST RADIO EQUIPMENT

NEW NA -AU) ADAPTER THE adapter shown in Fig. 1 is a

product of the Alden Manufacturing Co., and is designed to test the latest tubes in conjunction with tube testers and analyzers. As may be seen, the adapter has a five -prong base which connects through a suitable switching arrangement to the four sockets on top. The type 82 and 83 tubes are tested in

GRID CAP

'33.49,46 2. 59.5

PZ. GA LA

55.85. 2969 WUND:A WUNDB

Fig. I

The new Na -Ald adapter used for testing all new tubes.

the four -prong socket (each plate tested in turn by means of the toggle switch);

type G -2 and G -3 tubes in the UY socket; and 41 and 42 tubes in the six -prong socket. One of the sockets is a combination 6- and 5- prong; in the five -prong socket, all pentode, 46, 49, and 52 class B tubes are tested. The type 59 tube is tested in the seven -prong socket. Facilities are also included for testing the 29, 55, 57, 58, 69, 85, and 89 tubes.

NOISE ELIMINATOR STATISTICS, obtained by leading

radio engineers, show that most of the noise picked up by the average broadcast receiver is due to the lead -in. In order to minimize this noise pickup Amy, Aceves and King have developer a matching transformer, shown in Fig. 2, which is inserted between the antenna and the shielded lead -in, as pictured. The lower lead -in impedance reduces noise.

READRITE PLUG IN line with the campaign for modern-

izing old set and tube testers, the Readrite Meter Works announces a new line of adapters suitable for such work. Fig. 3 illustrates a new plug to be used at the end of tester cables for testing all new tubes.

Of particular significance is the latch which is especially useful. The plug shown is known as the type 66 and may be used with Readrite or any other type set tester.

TESTER PLUG THIS, and the past two issues of

RADIO -CRAFT have contained descriptions of adapters suitable for modernizing almost any type of tester. The device shown in (1) of Fig. 4 is a photograph of one of the units. It has a five -prong base and a six -hole top; a 6- inch lead projecting from the socket facilitates connection to the tube cap.

NATIONAL S.W. COILS ITEM (2) of Fig. 4 is one of a new

series of S. W. coils produced by the National Company. Since the advent of the new 57 and 58 type tubes, there has been very little data available on coil construction suitable for these tubes. The coil shown has a primary, secondary and tickler winding, and connections are made to a six -prong base. Thus the coil may be used as either an antenna coil, or R.F. transformer with or without regeneration. The same coil is suitable for both the 57 and 58 type tubes. A National socket must be used, since the pin spacings are not standard.

AN S.W., R.F. CHOKE

SHORT -WAVE chokes have always

been a problem. The National Co. has solved this problem by designing the unique choke shown in (3) of Fig. 4. It consists of four narrow sections, each universal wound, spaced on an Isolantite form. Although the chokes are supplied with stiff leads for mounting, they may be placed in standard grid -leak clips.

LAPEL MICROPHONE

ITEM (4) of Fig. 4 is a photograph of

a new lapel microphone manufactured by the Miles Reproducer Co. They are made in 100- and 200 -ohm sizes to suit individual conditions; a two -button type is also made. It is finished in high chromium; weighs approximately two ounces; and the stretched diaphragm is of a special alloy which is finished with a 2234 - karat gold plating. It is sensitive; works with 2 to 8 ma.; and has a flat frequency- response curve.

UNIVERSAL SOCKET AUNIVERSAL socket, taking four -,

five -, and six -prong tubes is one of the latest items by Na -Ald. This universal socket is shown in Fig. 4, item (5). While most set testers are equipped to handle four- and five -prong tubes, they sometimes require so many adapters that the adapters weigh more than the tester itself!

The socket illustrated, then, is suitable for installation in all types of equipment that continually use multi - prong tubes. The fact that it saves space is obvious.

Fig. 2

The noise -free antenna equipment by Ames, Aceves and King. A shielded lead -in is used.

332

Fig. 3, above The new Readrite plug

with special latch.

Fig. 4, right An entire line of brand new items for the Service Man or experimenter, Plugs, coils, special S. W. chokes and micro-

phones are offered.




NOISELESS ANTENNA SYSTEM FIGURE 5 is a device that Service

Men have waited for with some impatience. It is a device that, when connected to a shielded lead -in, reduces the noise picked up by the antenna system. How?

A CODE TEACHER THE device illustrated in Fig. 7 was

designed for the man who wants to be "tailor made." It is a self- teach- ing code practice set. An audio oscillator has its output varied by the practice key, which results in a record being made on a tape which may be played back in the same machine, and heard. A product of Teieplex.

Fig. 5. Photograph of the Pacent Radioformer.

ANT

SHIELDED LEAD -IN

Fig. 6. Suggested schematic circuit of the Radioformer.

Well, it is a known fact that the lead -in picks up the greater part of the energy called noise. This may be obviated by shielding the lead -in. To reduce capacity effects, the Radio - former, a product of the Pacent Elec- tric Co., is interposed as shown in Fig. 6.

Fig. 7. The Teleples code practice set.

THE SYNCROFILM PROJECTOR APORT ABLE sound projector,

weighing but 60 pounds, has recently been developed by the engineering staff of the Weber Machine Co., and is pictured in Fig. 8. It is complete in every detail, and is equipped with amplifier, speaker, sound head, etc. The beauty of the device is that it may be set up in almost any location demanded by circumstances.

THE WONDER "BAR" RECEIVER THE very unique radio set pictured in

Fig. 9 was designed to serve a double purpose -a radio set and dispensing bar. When closed, it appears as shown to the left, and when opened, it appears as shown to the right. When in this latter position, the "dispensing" part is ready for action.

The receiver is made in several types: The first, known as the 51, is a combination bar and radio operating from 110 volts A.C., and covers the range from 150 to 550 meters; the model 46 operates from D.C., covers the same range, and uses the type 14 tubes in the R.F. end of the set. They are products of the Wonder Bar Radio Corp.

Fig. 8, left. The Syncrofilm projector ready for action. Fig. 9, above. The Wonderbar receiver. At the left, the bar is closed; at the right, the bar is open. Please note the brass rail!


A REMOTE -CONTROL TUNING UNIT

REMOTE-CONTROL tuning has long since passed the luxury stage. In

fact, in many installations, Service Men have found them absolutely necessary in order to effect a good installation. Fig. 10 is an example of such a unit, designed for installation by Serv- ice Men, which may well be incorporated in the kit of tools. It is a product of the Federal Telegraph Co.

Appended here are some of the features of the control device: Operates through one standard cable length, 25 feet long; operates independently of the set; turns the set on and off; controls volume; easy to install; has no electrical contacts; has no motor; and no complications at all.

Fig. 10. The Federal, remote -control tuning unit.

A DIRECT -READING OHMMETER

THE new point -to -point method of

measuring resistance has created quite a demand for portable ohmmeters. The instrument illustrated in Fig. 11, manufactured by the Westinghouse Electric and Manufacturing Co., has just been announced. It is equipped with resistance ranges of 5,000 and 50,000 ohms, and operates directly from a single dry cell. The current consumption is so small that the life of the battery is said to equal its "shelf life."

Fig I. The Westinghouse ohmmeter. The toggle switch selects the proper range.

333



NEW TUBE ANNOUNCEMENTS This month's allotment of tubes is varied. First, we have a power -output pentode

for D.C. operated receivers; then a W.E. tube for amplifier work; a new power

amplifier and modulator; and finally, an output pentode for standard, 2.5 -volt use.

CONTROL- GINO --

RADIATOR

SCREEN- GRID

CONTROL - GRID

RIBBED 5l1RGACE

SCREEN- GR,D

PLATE - CONTROL- GRID

Ts-CATHODE

HEATER - L HEATER

(BOTTOM VIEW OF BASE)

Details of the Fig. I, above

internal construction of the 48.

Fig. Z lower Tube pin connections of the 48-a bottom view.

ISO 22 Ef s S0 vOnS CONTOL GRID G VOLTS Ea 0`V SCREEN VOLTS 95

.1-.:ii::::ñi 1r4 lí..1...1.1... ori EY,i.==-° pFS ".a .I..\aroÿ -:Gi.ii.

E............ i '-e CflC=..

woo.-- -r% F. ...-- io - xD

'mini.. -25 rimas---- ..81EiiO.i o0 .p. 30 . -- i- 4s ... -35 1---a.-------üilüi -

0 100 150 200

PLATE VOLTAGE

250

Fig. 3 Plate -voltage -plate -current curves of the 48 with various grid biases. Note the load line of 2,000

ohms.

Of

2

9.000

ao00

MOO ó i 6.000

W

= 5800

Ñ 4.000

ñ 3.000

W

2000

Ef30VOlTs

30

20

Io

SCREEN VOLTS9S PLATE VOLTS 95 1 11 MM AMPLIFICATION 1 \1 :: FACTOR .u.so 111

PLATE uuuuuu1 RESISTANCE 1I 11111M2 1111d IMMI ' I1

UTUAL ETAMEM CONDUCTANCE gm 11 /AMA 1 77 LVV I' 1 Ì 1 I4 O d L \ % 11

MPAOMIIMOMMO .ri Rid UU 1111 11111

-40 -35 -30 -25 -20 -I5 -10 -5 0 CONTROL- GRID VOLTS

i

Fig. 4 Dynamic characteristics of the 48.

334

LOUIS MARTIN

IT HAS been the general contention of engineers and Service Men for many years past that D.C. power - operated receivers could never pro-

duce the same undistorted output as the standard A.C. operated receiver. This has been true for many years, but since the recent numerous additions to the tube line include tubes especially designed for D.C. operation, the above statement no longer holds.

The 48, Power Output Tube

The most recent tube announced at this writing is the 48, pictorially shown in Fig. A. The dome -shaped envelope is more or less familiar to us since the arrival of the 58, but, in this instance, it serves another function. As illustrated in the photograph, at the top of the tube a large star -shaped mica disc separates a cylindrical plate at the ex- treme top from the remainder of the

48 A power- output pentode. Filament voltage, 30; filament current, .3 -amp.; power output, 2.5 watts; plate voltage. 100; screen voltage, 95; plate current, 50 ma.; screen current, IO ma.; grid

bias, 21 volts.

elements. The edges of this disc are tightly pressed against the dome shaped top for support. A diagram illustrating the internal construction of the tube is shown in Fig. 1.

This 48 may be described as a power amplifier tetrode having pentode characteristics at the recommended screen and plate voltages, for use in supplying exceedingly large power outputs from receivers designed for operation on a 115 -volt, D.C. power line. The main feature of this type of tube is its ability to deliver power at the low plate and screen voltages obtainable from such service. In fact, two type 48 tubes in a push -pull circuit are capable of delivering an output equivalent to 16 type '38 tubes!

The large power -delivering ability of the 48 is made practical by the unique features of its electrical and construe - tional design. Among these are the big cathode with its large emitting surface; the control grid structure with its heating radiator (which is the small cylindrical plate at the very top of the tube); and the plate, which has a ribbed structure fastened to its inner

surface. The ribbed structure serves to suppress the secondary emission which limits the power output of the usual four -element tubes. It might be well to add that the large amount of heat dissipated in the cathode also, of course, heats the control grid and means must be taken to cool this grid. Hence the aforementioned structure in the dome of the tube which is nothing but a heat radiator for the grid.

The heater of the 48 is designed for series operation at 30 volts, therefore permitting the design of a circuit using two of these tubes in series which will require a minimum of auxiliary resistance in the heater circuit with a conse- quent reduction of heat energy to be dissipated in the receiver.

The base pins of the 48 fit the standard six -contact socket which may be installed in either a vertical or hozi- zontal position. A schematic circuit

262A An amplifier triode. Filament voltage, 10; plate voltage, 180; grid bias, 7.5

volts; filament current, .3 -amp.; plate current, 3 ma.; plate resistance,

16,000 ohms.

showing the design of the base of the tube is illustrated in Fig. 2. This view shows the base of the tube looking up. It might be well to mention at this point that although the heater of this tube is designed for 30 -volt operation, it is possible to operate a receiver using these tubes in a location where the line voltage fluctuates so that the voltage at each 48 may vary from 26 to 34 volts.

In a series heater circuit employing several 6.3 -volt tubes and one or more 48's, the heaters of the 48's should be placed on the positive side of the line potential.

As a class A amplifier, the 48 is recommended for use either singularly or in push -pull in the power- output stage of D.C. receivers. If a single 48 is operated self- biased, the self- biasing resistor should be 360 ohms. This resistor should be shunted by a suitable filter network to avoid degeneration effects at low, audio frequencies. The use of two 48's in push -pull, of course, eliminates the use of shunting the resistor. The self- biasing resistor required for the push -pull stage is ap-




WHERE TO USE THE NEW TUBES

THE 48 is a power -output pentode for use in D.C. operated receivers. It has a 30- volt filament and is designed to operate in series with the usual 6.3 -volt automobile tubes. It has an output equal to 8 type '38 tubes. The 262A is a Western Electric three -element amplifier tube designed for use in audio amplifier circuits. It is rugged and non -microphonic. fhe 842 is an amplifier- modulator tube suitable for transmitting purposes, or in high - powered audio amplifier systems. The 59 is a 2.5 -volt power -output pentode for A.C. operated receivers. Three separate grid connections are brought out to facilitate its use as a class A triode, a class A pentode, or as a class B triode.

proximately 180 ohms. Any conventional type of input coup-

ling may be used provided the resistance added to the grid circuit by this device is not too high. This is in direct contrast to the usual arrangement where high input impedances are demanded, except in class B tubes. In any case, the sum of the resistance of the coupling device in the grid circuit and the resistance of the filter network (if used) should not exceed 10,000 ohms.

Figure 3 shows the relation between plate current and plate voltage at various grid potentials. Note particularly the absence of the "hump" at low plate voltages which is so predominant in the ordinary four -element tubes. Figure 4 shows a set of curves of the variation of its dynamic characteristics. A receiver using this tube is described elsewhere in this issue and the writer

842 Amplifier -modulator. Filament voltage,

7.5; plate voltage, 400; grid bias, 80

volts; plate current, 30 ma.; undistorted power output, 3 watts; permissible

grid swing, 80 volts.

wishes to state that it is only by hearing a receiver using 48's that one may appreciate the tremendous gain over its predecessors.

The following ratings and characteristics obtain: Heater voltage (D.C.), 30 volts; heater current, 0.4 -amp.; plate voltage, 95 to 125 volts; screen voltage, 95 to 100 volts; grid bias, -20 to -22.5 volts; plate current, 47 to 50 ma.; screen current, 9 ma.; plate resistance, 10,000 ohms; amplification factor, 28; mutual conductance, 2,800 micromhos; load resistance, 2,000 ohms; power output (9% total harmonic distortion), 1.6 to 2.5 watts.

The Western Electric 262A

Of special importance at this time is the announcement of the characteristics of the Western Electric 262A vacuum tube -a three- element tube having an indirectly heated cathode which permits operation of the heater element directly on A.C.

It might be well to state that this tube cannot be purchased by the ordinary broadcast listener or Service Man. It is designed for use in equipment

RADIO -CRAFT for DECEMBE

manufactured either by the Western Electric Company or by the American Telephone and Telegraph Company, but may be secured by any person licensed by the Federal Government to operate an amateur radio telephone station.

The following ratings and characteristics of this tube, illustrated in Fig. B, obtain: Heater voltage, 10 volts A.C. or D.C.; heater current, .29- to .35 -amp.; maximum plate voltage, 180 volts; grid bias, -7.5 volts; average plate current, 3 ma.; amplification factor, 15; plate resistance, 16,000 ohms. The low interelectrode capacit- ances listed below should make this tube suitable for short -wave work: Plate to grid, 1.9 mmf.; plate to cathode, 4.0 mmf.; grid to cathode, 1.8 mmf.

The 842 Power Amplifier and Modulator

The 842 is a three electrode, low -mu,

59 A power -output tube. Has individual grid connections. Filament voltage, 2.5; filament current, 2 amp. The ratings of this tube vary, depending upon the mode of connection; see text for

detail ratings.

high vacuum tube designed primarily for use as a class A power amplifier, and as such is particularly useful as a modulator tube in amateur transmitting equipment. In general appearance and filament characteristics this tube resembles the '10, as shown photograph- ically in Fig. C. There are very few unusual features about this tube, but there are several points which should be given detailed consideration.

The grid return as well as the plate return circuits should be connected to the mid -point of a resistor placed across the filament winding of a transformer. If operated from D.C., these returns should be connected to the negative filament terminal. In cases where the 842 is employed in resistance- coupled circuits, the recommended safe maximum value of grid leak is 1. megohm if the self -bias method of obtaining grid voltage is used. Values higher than this may so aggravate any slight trace of gas or electrical leakage existing in the grid filament circuit as to start a small grid current with the result that a voltage drop opposed to


R, 1932

The figure numbers from left to right are A, B, C, and D. Fig. A is the 4111, D.C. operated output pentode; Fig. B is the new W.E. amplifier tube; Fig. C, the amplifier- modulator tube; and Fig. D,

the 59, A.C. operated output pentode. (Photographs courtesy R.O.A. Radlotron. western Elec-

trir. and National Union.)

1l®,N .I 7li. GRID VOLTS II1 Ts .II18.1 . /If o 11 Its 130 /III vo EMMA -ITs 11III*E. IiIIlI /m.11 .ra IMAMS' t00 MM/1n v IIhI/111 U1I7Ilh~R //II/II

IMO AIM Nib lIIwAII .IIIrIIII\Qqb hILIII 111'IIII11/ 1I/.IIII IIIII'IIII Lk,, IIIII I4I/IIfIII1\.s ./,II rIIIR%OMI%O4/A

Fig. 5

Plate -voltage- plate -current curves of the 842, amplifier or modulator tube. ' --MOD PLATE MDpuLATOa PLATE

DISSIPATION LIMIT MILLIAMPS. BImanna I WW mom/Lew'

MoDULATION Pa TOR eO.) \ lc íZ:AS`..m

sae ts 6i%ÌI ®C29SGORC.-_-. iSriAl6ir¢7íiM mGm/9r4s70 6676) Ii C%r .6pír!aei;Sa...

. 'SasaBIISi88 loo zoo soo 400

MODULA ION PLC E VOLTS 500

Fig. 6

Curve showing the relation between required oscillator input watts and required modulator plate voltage for the modulation percentages (indicated by the solid lines) and plate currents (indicated

by the dotted lines) shown.

25

26

z =4

22

ve 20 ó b n E,

M = 12 ú6) r

6

4 2

o

NMWL I OUO , v E : ll

a

ITOL.

, !CLASS

,

MN PULL AAA ' PeeN-PUSH

CLASS

PUSH PULL 1 !VIII 1 PeMTODe EMI Ni! 1111

.fi1: m IIG1f1f1111

1IIIÌ111Ì/ `1'

V inIIII mituUll I// 661

=111111= IE01111I 86111 r41 111

a_ %4E

111111111il11111/!R': mm...e_:::;1':inlill

WIN mom 2. WATTS

to 40

Fig. 7

Three excellent curves showing The relation between distortion and output power for the 59 connected either as a push -pull pentode, a push -pull class A

stage, or as a push -pull class B stage.

335



View of the completed apparatus showing the layout of all parts.

ARMATURE ARMATURE SPRING A 1

MI BRASS BAR

me

- CONTACTS

9l-Q

O CONTACTS

ARMATURE \A2 SPRING ARMATURE

Fig. I

Schematic of the circuit breaker.

n ROO

- SuPPORPNG -_ ANGLES

F

HARD RUBBER

ARMATURE

aa

ROO

BRASS TUBING

-CL 2

Fig. 2

Diagram showing the connection of the motor and filament- cut -off relay.

FLEXIBLE Ir METAL

A STRIP

HIN. /

CONDENSER SHAFT

FLEXIBLE METAL STRIP

1

R D

MA%.

SMALL \ -. COIL

JUMBLE WOUND

TO CABLE

4.5V

!1I0I

ARM HIGH

FREQUENCY BUZZER

Fig. 5 The method of connecting the buners to indica when the tuning tond has reached the ex-

tremities of its range.

336

BUILDING A

REMOTE CONTROL TUNING SYSTEM C. H. WEST

ACASUAL glance at the accompanying photographs and schematic diagrams will impress the layman and reader that

what follows represents a highly complicated system, and involves too much work. This is not the case. Most of the equipment may be found around any amateur workshop, and consists of a few old buzzer magnets, worm and worm wheels, and a driving motor.

Remote control transmitters are considered t h e desideratum of a good station; but o u r opinion is that the operator should be where t h e transmitter is; while the receiver should be located at almost any distance ranging from feet to miles. With this idea in view, this remote control unit was conceived, put into practice, and found ideal for either amateur or professional use. With a few slight modifications, it is adaptable to the broadcast receiver.

Suppose we examine the fine points of this apparatus without going into the details of construction. We find - that by pressing buttons No. 1 and No. 2 together, the filaments of the receiver are active, and the driving motor becomes activated while idling. We press on button No. 1 and the variable tuning condenser starts to rotate slowly from the minimum towards the maxi-

mum capacity. We hear a station and let up on the button. The station stays there. Again we press on the same button and tune in another station - and so on.

Now, we press on button No. 2. The tuning condenser reverses

its action from maximum to minimum, and we are able to come back to any previous station just heard. However, the volume or regeneration does not seem to be quite right or of sufficient strength. We press on button No. 3 in form of a "dot." This steps up a very small degree of regeneration, and if it is not sufficient, we follow up with as many "dots" as necessary (which are not many).

We wish to discontinue operation of the receiver. Simply press on buttons Nos. 2 and 3. The filaments are ex- tinguished, and the motor stops. We now examine our operating table and simply find three small push buttons. Even the telephone receivers are with us. There is a small remote control indicator in front showing the degree or any caption representing volume or regeneration. There is still another indicator, which tells us when we are at the minimum or maximum range of the tuning condenser; and all remote control.

Then we examine the cable which leads from the receiver to our table. Our surprise is still greater. We find just four wires. How can a receiver operate at a great distance with so few, when indicators, tuning, volume, phones, "B" power, cut -offs and ons- are all located somewhere within the tangled mess. We are very much interested and grab the main diagram of the "works"; and after tracing out a few leads, exclaim: "How simple!"

FEATURES OF THIS REMOTE TUNING DEVICE

Electrically operated; uses dry cells; em-

ploys ordinary household bells and

buzzers for the relays; may easily be

constructed at home without any intri- cate machine -shop equipment.

BACK -LASH STOP

TUBING RASING BEARING _ REARING

/ RATCHET \I

RETURN TJ MINIMUM CAPACITY ESCAPE- MENT NO PIN

SNAr'T

RATCHET \L KICKER

/_ CONTROL MAGNETS

ARMATURE i

T U". SWINGING / CIRCUIT BREAKING BOOK TYPE

BEARING ARM CONO

RATCHET STROKE ESCAPEMENT ESCAPEMENT REGULATOR AND PIN ARMATURE STOP

I BACIoLASM ySTOP

CONTACTS

CIRCUIT BREAK-

ING

r ss

ARM p DETAIL A DETAIL 9

A

Fig. 4 Diagram of the arrangement of the regeneration o

volume -control unit.




Complete constructional data of a new

remote -control tuning system that may

easily be built at home by any amateur.

It tunes, controls volume, and shuts the

set "on" and "off."

Therefore, leaving out the fine points and reserving same to illustrate the text and constructional data, we will take up the first step in construction, which deals with the "Circuit Break- ers" and "Relay"- although the simplest are most important.

Circuit Breaker Unit No. I

This circuit breaker consists electromagnets of the bell or buzzer type. They are rewound with the same number of turns of No. 20 D.C.C. wire. The metallic core should be well insulated to prevent a short circuit between the windings and the core. In the center of each core a small hole is drilled and a contact point of silver or iridium installed. The two magnets should not be fastened together by their riveted ends, but to a strip of heavy brass. The charging of one magnet should not affect the other. The armatures should be of flimsy material; the soft iron cores of old audio-frequency

of two

transformers are very suitable. Each armature should have fastened to it a thin strip of spring brass. The object of this is to operate the armature with the least amount of pull; as each one of these electromagnets are in series with the main tuning -control magnet.

A contact point is located in the end of each armature, and adjusted just close enough so that exterior vibra-

tions will not close the contact.

From an examination of Fig. 1, it can be seen that any power applied to "Ml" will actuate armature Al, and the same applies to M2 and A2; and if power is applied to b o t h magnets, both

Al and A2 will close. The reason for the use of larger wire in these magnets is to reduce its resistance and not cut down the flow of current through them. This unit may be mounted on the same base with all other apparatus.

Motor and Filament Cut -off Relay This relay, Fig. 2, consists of two


WHAT THIS DEVICE DOES

From any remote point which is connected to the radio set by a 4 -wire cable, this tuning device does the following: (I) Turns the radio set "on" or shuts it "off"; (2) Raises or lowers the volume at will; (3) Tunes the radio set

to any desired point.

Tw WORM AND WORM ADJ x[ECONDENS CONDENSER

,8 SCREW

CHECK NUT' y BRACKET -w

PIVOT BEARING

BEARING GUIDE

AO! i HANGER

- COLLAR

SLIDING BEARING

BEARING GUIDE

Fig 3, above Diagram showing the connections and mechanical arrangement of the tuning -control relays. When magnets Ml are excited, the shaft is pulled to the right, revolving the right -hand, flat -faced pulley.

Fig. 6, right Complete schematic circuit of the remote -control tuning unit. The three remote -control buttons are shown at the upper left; the four -wire cable to the unit itself connects to these buttons. The

meter shown is not essential.

View of the completed equipment with the cover closed.

The volume -control unit. Detail drawings are given in Fig. 4.

Close -up view of the volume -control condenser shown schematically in Fig. 4.

13000 I

MS TELEPHONE RECEIVER

2(1, 3o I REG. INDICATOR IN SERIES

REMOTE SECTION

o COND. SHAFT

-1 COLLARS /\

i I

TUNING ING.CATOR / \m:, -aye -A Ca,oe view -

t SHOWN PM CLARITY)

32 PITCH r I

BEARING

REDUCING GEARS ' l

®II 1M .

FILAMENT

SLIDING BEARING AND BEARING

GUIDE \

10 V. AC.\ MOTOR

PULLEY I I

Ce0SS _ BELT

`BEARING

16 T1CH

BEARING

:a PIVOT BEARING

AMC

1 I10 V, A c

el

M3

BUZZER ÑÑ E- D-BREAK

LEAD

r x

RUBBER TIR o

r

o in

~ BEARINGS

WITH COLLARS

4 Q +0

1 rU4ET

DRY-CELLS 1G VOLT

STORAGE BATT

s

0000

SWINGING

6-00.0

BEARING

CIRCUIT BREAKER

T

TD POWER

AMPLIFIER




RED LEAD

BLACK LEAD

Fig. A External view indicating the layout and stressing the important points of

construction.

Under- chassis view Fig. B

All small condensers and resistors are placed as close to their terminating points as possible.

HOW TO BUILD THE

SAVIL TYPE 746

D.C. KIT -SET

B. S. VILKOMERSON*

WHY YOU SHOULD BUILD THIS RECEIVER

Tests in our own laboratories convinced us that

this set has as good quality as any A.C. operated

receiver costing three times as much as the Savil

receiver described here.

The parts for this receiver may be purchased,

complete, for about $20.00. All parts are standard,

and may easily be obtained on the open market.

With an antenna consisting only of the human body,

local stations were brought in with tremendous

volume; in fact they could be heard, easily, a block

away! Although distant stations were brought in

without any trouble at all, there was absolutely no

interference from the locals mentioned above -and in the daytime, too!

Without any hesitation, we say this is one of

the best D.C. operated receivers that has come

to our attention.

TWO type "48" tubes equal 16 of the older, type '38 tubes! In this single sentence is contained the outstanding feature incorporated in the distinctly new receiver de-

sign illustrated in Fig. A; an underside view is Fig. B; in Fig. 1 is shown the schematic circuit.

The writer presents to the (hitherto unfortunate) residents of D. C. districts a direct- current set which gives results in all respects as good as those obtainable from an A.C. receiver. The "brand new" type 48 tube has now made it possible for the radio receiver manufacturer to make a moderately - priced set operating from the D.C. line which compares very favorably in A.F. output with the standard A.C. sets. The power output of two or three tubes in push -pull is 5 watts!

Some idea of the power output at 100 V., plate, may be secured by consider- ing that it would require more than 16 of the older, type '38 pentodes to equal the performance obtainable from two, type 48's, as illustrated pictorially in Fig. C.

The Savil Type 748 D.C. Kit -Set was

In charge of engineering. Savii Radio Engineering Corp.

338

designed to secure the advantages of the type 48 tube, by arranging the circuits to fit its special characteristics.

Perhaps the best way to describe the 48 tube is to compare its characteristics with those of the better known '47. Both are A.F. power tubes of equal output; but whereas a single '47 gives 2.5 watts output with 250 V. on the screen -grid and plate, a single 48 gives 2.5 watts with 100 V. on the screen - grid and only 125 V. on the plate. The '47 is a pentode, the five elements being the filament -type cathode, control -grid, screen -grid, suppressor -grid, and plate; these connect to a 5 -prong base. The 48 is a tetrode, with heater -type cathode, control -grid, screen -grid, and plate; these terminate at a 6 -prong base. The function of the suppressor - grid in the '47 is performed In the 48 by a special rib structure welded to the inner surface of the plate. The cathode has an unusually large emitting surface, the heater taking .4 -amp. at 30 V.; (12 watts power consumption for the heater of the 48 as compared to 4.5 watts for the filament of the '47).

This high heater voltage is helpful on D.C. sets, as it makes a minimum of additional resistance necessary in the

series filament circuit. This advantage is clearly indicated in Fig. 2, which shows the voltage drop across each filament in the series; the "bleed" current is put to use in the field coil. Re- sistor R15 and pilot light V8 pass the added current required by the push - pull 48's.

Other characteristics of the 48 which influence set design are its lower amplification factor (mu28) as compared to that of the '47 (mul50), and the makers' specification of a maximum of 10,000 ohms resistance in the external part of the control -grid circuit. This limits the types of input devices which may be used to either transformer or impedance coupled units. These factors, in turn, make it preferable to use a triode as the tube preceding the 48.

A description of the audio end alone would suffice to give the necessary information regarding the use of the 48, and it actually is only the correct use of the 48 which gives this receiver its exceptionally good volume and tonal quality. When the writer found how well the output from the audio system compared with that obtainable from good A.C. sets, he decided to go the rest of the way and use an R.F.

RADIO-CRAFT for DECEMBER. 1932



end which would give the additional selectivity and sensitivity warranted by the greatly improved audio system.

As can be seen from the diagram, a four -gang condenser is used, the first three tuned circuits being the inputs of three type '39 multi -mu R.F. pentodes, while the fourth is coupled to the control -grid of a type '36 screen -grid detector. With properly designed coils, this R.F. arrangement will give adequate selectivity and far more than enough sensitivity to go right down to the noise level in even the best locations.

It need hardly be mentioned that D.C. locations are usually much worse than A.C. for noise (due to the spark- ing of commutator equipment), so that the maximum useful sensitivity is usually quite limited. Some radio men still have the notion that "a sensitive set brings in too much noise" in a noisy location. This is true only to the extent that a more sensitive set can bring in more noise in a noisy location; but in comparing a set having a high maximum degree of sensitivity with a less sensitive set, at any location, it will always be found that any station that can be tuned in on the less sensitive set can be brought in on the more sensitive set at exactly the same volume with neither more nor less noise, the audio frequency response range of the two sets being equal. (Of course, a set that "loses" low notes and high notes also "loses" some static.) On the other hand, wherever and whenever noise conditions are not particularly bad, the more sensitive set will bring in more stations.

Again, in many D.C. locations the installation of an adequate antenna system is impossible, in addition to the field strength of the broadcasting stations being low on account of the shielding effect of intervening steel struc- tures. In such cases, a very sensitive set used with a short piece of wire hung outside the steel building will often give surprisingly good results, since the steel structure of the building acts as a grounded shield to keep the electrical noises generated by de-

(1Zr

Fig. C

2 TUBES 16 I REPLACE The enormous power output of this re-

ceiver is due, in part, to the use of the

new type 48 tubes, described elsewhere

in this issue. This is illustrated above; the

two 48's are shown above the 16 type '38 tubes -the undistorted output of both groups being the same!

Those in D.C. districts have no need

to anathematize the scratchy output of

D.C. receivers -not with these tubes.

In fact, the amplification is so great in the audio amplifier that a phonograph may easily be connected to the terminals provided to secure clear,

undistorted reproduction.

f-1

'39 '39 '39 '36 '37 48 48

V6 V7

PILOT LIGHT

V8 I- --30V. 60V.

120V. 1.-30V-.1 REPRODUCER -,-FIELD FIELD Coa

Fig. 2

Circuit illustrating the wiring of the filaments.

vices inside the building from affecting the aerial wire outside! Of course, any lead -in wiring inside the building picks up noise, and therefore should be kept down to a minimum length. However, the real job will incorporate one of the modern R.F. coupling systems.

It will be noticed from the diagram that some manufacturing economies in R.F. bypassing are affected by using cathode, screen -grid and plate voltage supplies common to two adjacent R.F. stages. Since any R.F. voltages across these bypass condensers are of opposite phase, any common coupling is of a degenerative nature, thereby giving added stability. The third R.F. stage, whose R.F. currents would be in phase with those of the first stage, has de- coupling resistors in the voltage supply lines, and separate bypass condensers to the ground point.

Another innovation is the use of a dry, non -polarized electrolytic condenser in the D.C. filter system !; (both electrodes are formed). The usual polarized electrolytic condenser would be destroyed if the line plug were inserted the wrong way. A paper condenser of equal capacity would be much bulkier and cost several times as much as the non -polarized electrolytic unit, which gives equally good results.

An idea of what degree of selectivity may be expected from this set may be had from the fact that in down -town Manhattan it was found possible to bring in WJR (Detroit) operating on 750 kc. and WBBM (Chicago) operating on 770 kc. with little or ho interference from the local station WJZ operating on 760 kc.

This degree of selectivity is due in no small measure to the design of the R.F. transformers. The primary of Ll has 8% T. of No. 26 S.C.C. wire, spaced two turns, and wound over the filament end of the secondary; the primaries of L2, L3, L4 consist of 50 T. No. 32 S.S.C., solid wound over the filament end of the respective secondaries. Each primary is spaced from its secondary by three layers of Empire cloth. Each secondary consists of 127 T. No. 32


R

RED LEAD

C9 LI ' RFl

MANUAL VOLUME CONTROL

CIO OLACH LEAD

EXTERNAL ONO. _r

C1t

PHONO. PICKuP TONE CONTROL ( T1

i L2 R F 2 L3 R F 3 L4 DU

RII C20 A F.1 `f-ï 1 39 36 . 1 R12 '3 ^---

J%ii

I

Eti Ia I

L! -C4

eil7 1E, C2I

Cl6 R Rl3'

C12 s g 6v PILOT

LIGHT .IS -A.

A.F. 2

PUSH -PULL 48's

1

e R2

C22

CNT.s

REPRODUCER

T2

1-

R14

VOICE COIL

75

Sw

C23

CHAS515 Rl ANO 5w ARE COMBINCO NON -POLARIZED DRY ELECTROLYTIC

OHMS

110V, _ DC.

Fig. I

Schematic circuit of the receiver. Variable -mu tubes, push -pull 48's, tone control, terminals for phonograph pickup, and non polarized electrolytic condensers are some of the features of the receiver.




Fig. A above An external view of the 2 -volt receiver described

by the author.

Fig. B below An under -chassis view showing the layout of the

parts.

THE 2 -volt superheterodyne illustrated in Figs. A and B is an up- to -date battery receiver incorpor- ating 2- V- filament tubes in a care-

fully designed, modern circuit, Fig. 1. This receiver is highly suitable for use in the home, especially where house - lighting current is not available. In such cases, the filament current may be supplied by dry cells or a storage battery.

The 2 -Volt Superheterodyne also makes an excellent portable, since it is light, compact, and powerful and has a high degree of sensitivity; install the batteries and speaker in a separate carrying case. The total filament drain is 880 ma.

The first detector, V1, uses grid - circuit rectification thus insuring maximum sensitivity. The oscillator, V2,

CONSTRUCTING A 2 -VOLT

SUPERHETERODYNE A description of a 2 -volt receiver of the superheterodyne type capable of excellent quality, volume, and distance.

H. G. CISIN, M. E.

FEATURES OF THIS RECEIVER Uses push -pull output; hence has

excellent quality and volume. Variable -mu tubes minimize in-

terference. Being a superheterodyne, it is ex-

tremely sensitive. Operates entirely from batteries,

and therefore may be made portable.

Economical in operation. Low cost of construction. Ease of operation.

is coupled to the detector stage ca- pacitatively by means of condenser 7. Great care has been used in the design of the I. F. stages which are to be peaked at 465 kc. The selection of this high I. F. is desirable since this means a high oscillator frequency and hence fewer harmonics within the receiving range. This in turn results in a closer approach to the desired "one - spot" tuning. The type '34 variable - mu tubes used as V3 and V4 help to improve the characteristics of the I. F. amplifier. Since there are two I. F. stages with tuned grid and plate circuits, adjacent channel selectivity is sharp and clean -cut. The grid- return circuits of the two I. F. stages are carefully isolated thus preventing any tendency towards instability. Volume control is attained by varying the grid

bias of the two I. F. tubes, as shown. The second detector V5 is of the

power type. Its D.C. grid bias is obtained from the same source as the I. F. amplifier. However, its R. F. path is carefully isolated from the I. F. stages. The two -stage audio amplifier is of standard design. With the two type '33 pentode tubes in push -pull, the power output is slightly more than 1.2 watts. A magnetic speaker designed for use with these pentodes will give best results.

Individual amperites are used to reduce the voltage of a standard storage battery to the correct value for the 2- volt tubes. These resistors also improve operation by preventing voltage fluctuation, and furthermore, they act as fuses, thus preventing injury to the tubes through over -voltage. For complete protection to the tubes, Instru- ment Littel fuses should be incorporated in the "B" supply line.

The chassis material is drilled for all socket holes, including the one at the rear for the cable connection. It is then bent to the size specified at A in the schematic circuit, Fig. 1, and the sockets mounted. The two variable condensers are mounted as indicated in Fig. A. Next, the three I. F. transformers are fastened in place and finally the two binding posts.

The chassis is then turned upside down and the volume control 26 is


EXT. GNP

rt CHASSIS / 3y4

1 1

25

I F 2' '34,

DET. 2 AND A.VC

'30 )

29 32Í

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i + 38{ 39

A F. 2 PUSN-PULL

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40At

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_I MANUAL 12 CMA5L VOLUME

CONTROL

6

42 43 O O 44 45 0 0 46 47 c 49 50

"C--22I/2X. "C-'16%2v. "C+- "B+" 671/2V. `B+"135V. "A- B-" "A+" 51 e 52

SPEAKER

340

Fig. I

Complete schematic of the receiver. Complete isolation of the grid circuits is afforded by the resistors in the grid -return circuits.




Fig. A Panel view of the versatile, direct -reading, mutual

conductance meter designed by Mr. Potts

Fig. B

Under -Chassis view. The layout is self- evident

R2r

W 25

i' 20

1.5

210

.5 or

á .2 .5 A.S .6 .7 .8 .9 10 S RECTIFIED OUTPUT, MA..-D.C.

° Cl

I O

A.G,MA. FIL.

it TRANS.

L. wv.«1 A.C.

A

0-1 D.C.

A' MA.

RI 1 200 OHMS CURVE A

i 1250 OHMS CURVE B

R2. 0- 10.00 OHMS VOL. CONTROL

CI. 2MF.

/MI III ._ MMO

1,,,,,,,,,

Ittez 10e

> 1500>E 8

z 1200;61

800u,42 5 400g 2'j

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RADIO -CRAFT for

BUILDING A DIRECT -READING

MUTUAL CONDUCTANCE METER J. H. POTTS

An article describing the method of constructing a tube tester that reads the actual mutual conductance directly

IT IS the purpose of this article to describe the design and construction of a small, inexpensive tube tester which will read directly the

mutual conductance, in micromhos, of amplifying tubes of all types. It employs a new principle which makes its operations simple, yet precise. No mental arithmetic or "balancing out" operations are required. The apparatus is easy to make, and is adaptable to laboratory, shop or field service work.

It is possible to measure the mutual conductance of a tube in a particular set and under the operating voltages with which it will be used. Dealers and jobbers will find it indispensable for checking the uniformity of new tubes as its accuracy is such that it will discriminate between good and better tubes. Since the apparatus cannot be damaged by defective tubes, a separate set for shorted elements is unnecessary. In the field, the Service Man can make rapid tests of tubes in an operating set with a precision heretofore impossible with the usual type of analyzer, eliminating a large element of guess -work.

Analyzers are usually fitted with a 41/2 -volt battery for tube testing. The

plate current is read first with normal grid bias, then a second reading is taken with the grid voltage shifted 41/2 volts positive from the initial bias. The difference in the two readings is an indication of the tube's mutual conductance. However, tubes of widely differing plate currents may have the same mutual conductance; and with power tubes, with the meter shunted for the heavy plate current, it is difficult to determine how much change in reading takes place from the 4 1 -volt grid shift. Also, when there is a high resistance in the plate circuit the increased voltage drops due to the increase in plate current resulting from the grid shift voltage, makes any in- telligent estimate of the tube's condition almost impossible. Since even under the best circumstances the grid shift system involves mental arithmetic, the testing is slowed up considerably.

Fundamental Circuit The fundamental circuit used in this

mutual conductance meter illustrated in Figs. A and B, is shown in Fig. 1. Normal D. C. voltages are applied to all tube elements, but instead of using D. C. to shift the grid voltage, a small

(Continued on page 36.9)

4000 A OHMS

! 1,250 1 OHMS ,R3

125 V. 0'1 \Y yMEG. R4

R2

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0.1-MEG. RUED.

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10 M 15 15 12 r! ¡ i-- L 54. C4 SuF4'K F

-- F C J

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A{ t---äe I na-9 L- 31

1.14--1 7 10 6

TERMINAL 8 STRIP

i

14 RECTIFIER

1,250 UNIT N.

OHMS

SG \ 8 9

fW \I

R5 R6 2MF Cl

6 200 OHMS

9 11

10 I

9 8 4 5

1

3

1

0-1. MA.

KEY SwtTCH 5W.1

NOTE. NOTE SWITCHES A AND 8 MAY SW 3, C2, C3, C4

BE SUBSTITUTED FOR KEY HEEDED ONLY WHEN TESTING SWITCH SW.1 IF DESIRED TUBES IN RECEIVER SOCKETS.

Fg. I, upper left. Fundamental circuit of the tester. Fig. 2, above. Circuit diagram of the tester. Note that the terminals of the switches ere numbered.

Connect all points having the same number together. The terminal strip connects to a cable plug.

Fig. 3, left... Calibration curves of the tester for two values of load resistance.

DECEMBER, 1932 341



An example of the manner in which a flare is used on a loudspeaker. Note the depth of the horn.

(Courtesy, Hotel New Yorker)

SPEAKER. SUPPORT

This speaker is set in a box lined with hair wool to prevent sound from coming from the rear of

the speaker. (Courtesy, Hotel New Yorker)

+>o A b+ w ¿

P c

_

MI111M0I111.11.=N 11 1!IM.g1`i11R u.e-.. :-....e..,w,1 All t11 (xre mum r l - .i WG DE eDf erE I . 'C

. . lANIx -P A DM euf EAERE o1

->o 30 m soo i0o0

FREIDO QUENCY IN CYCLES PER se 4°°° ato

1 1 111 l I l i, f

1-

z+IO v

O

_A.' a 1 ' I_

fAI -. CURVE - rLAr earLLE Ilóllitllii - -6-.ILIeuLAAeuELE gro II I I t111 -m

so too 300 ipoo spoD FREQUENCY IN CYCLES PER SECOND

-g- SEARCHLIGHT -C-

' _ _

,1 LOOR

ANGLE HORIZONTAL

D15raiElUnON ANGLE

FLARE -V

.-,.j .

',Z.. HAIR -E- WOOL

-D-

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SPOT

Fig. I

342

SOME INTERESTING LOUDSPEAKER FACTS

This second of a series of articles tells exactly what the

baffle situation is regarding loudspeakers

ELI M. LURIE, B. E. E. PART II

C ORRECT methods of baffling are

undoubtedly the greatest hin- drance to the majority of radio Service Men who would endeavor

to produce an excellent sounding, public address system. It was shown in the preceding article that the formula for an effective baffle is

Eff. Baffle= Wavelength of sound in inches

4 In the past, this formula has been

used as an absolute criterion for every kind and shape of baffle. It was the last word so far as most loudspeaker installations were concerned. How- ever, the truth of the matter is that the formula is only applicable for Rat baffling and should not be taken as final where used with any other type of baffling arrangement.

In the July, 1931, issue of the PRO-

CEEDINGS of the INSTITUTE of RADIO

ENGINEERS, Benjamin Olney, well known loudspeaker authority, definitely showed that, as the size of the front of a radio cabinet was decreased, the low - frequency response also decreased.

This immediately would indicate that if a flat baffle of any size is broken up and distributed so that it takes the form of a box, or cabinet, then the low frequencies will depend almost directly on the size of the front panel; and, as this last item is decreased in size, with a corresponding increase in the length of the cabinet sides, then the cavity resonance will increase and will almost be proportional to added increase of the sides. This condition can be illustrated by referring to Fig. 1A, which was taken from Mr. Olney's aforementioned paper.

However, this does not mean that the formula is worthless and is not one to

so

d 45 m U 40

ó35

? 30 J

25

J 20

Ì 15

ZERO LEVEL -.006 WATTS DB- IO LOG 0166 06

111111111111111111111111MII 1111111IIIIII 11 111IIIIIII11IIIIII111l1 IIIII IIIII!11 1111IIIIIII111Eí11IlI II IIIINl1111111IIIIII II PE211111111111111111111M11

ii 10 > 1000 10 000 100 000

ROOM VOLUME IN CU F.T.

DI

100;

60,°n

20 á O

6.0 Ñ

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06 300.000

Fig. 2

Curve showing the relation between room volume and required sound level.

be used, for it can be applied with excellent results in places where flat baffling is used, and can be used for a rough check in almost all cases.

Suppose, fbr example, it is desired, in a certain building, to install a speaker such that with the given loudspeaker location to be somewhere on one of the end walls, and the height of these walls to be 20 feet, that all musical frequencies shall be reproduced, in their true fundamental tones, down to and including 50 cycles. Will the 20- foot wall be sufficient to reproduce down to 50 cycles? The room is 75 feet in length and 30 -feet wide. Where on the 20 -foot wall should the sound projector be located? Should it be nearer the top of the room, or should it be in the middle or near the bottom of the wall? What power level will be required to give good sound coverage and what kind and size of a power amplifier would you build to produce this level with a possible added safety factor of 507x? Why is it necessary to have an amplifier capable of delivering 50% more than the required room level? Also, what kind of a projector would you install?

Since the wall is flat, it would most certainly lend itself to baffle solution by means of the regular baffle formula. However, first it is necessary to change the frequency of the lowest desired fundamental to its wavelength in inches.

Wavelength in inches= 1,100 x 12

Freq. in cycles per sec.

and wavelength in inches =1,100 X12 _

264 inches Substituting this value in our regu-

lar baffle formula

Eff. Baffle= 244 =66 in. or 5' 6 ".

This means that in order to reproduce 50 cycles, our baffle would have to measure 66 inches from the center of the cone, around the baffle to the center of the cone in the rear, or 33 inches on a radius around the center of the cone. Therefore our 20 -foot wall would easily give us a fundamental of 50 cycles; in fact we could reproduce down to 13.6 cycles with such a baffle. In the case of a room wherein the speaker is mounted so that the front of the cone is completely isolated from the back,





A photograph of material having sound- absorbing qualities. In appearance it resembles ordinary corrugated board. (Courtesy Amy Aceves 8 King)

THE CAUSES AND CURES OF

AUDIO OSCILLATION A complete discussion of the causes and cures of audio oscil-

lation with special reference to public address systems

L. VAN DER MEL

-A-

IL

_

vt

To-c- 4 Ct

44----0r- u I ---, r' R1

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- _

Ó.1-MEG. .. BIAS RESISTOR

-B-

Fig. I

Circuit illustrating the manner in which oscillation may be generated by a common impedance. Al though oscillations w,ll be small when VI and V2 are successive stages, they will be great if VI is a

first and V2 a third stage.

MICROPHONE SPEAKER

--- INCIDENT INCIDENT_ \SOD

- AMPLIFÌER

MICROPHONE

1 SPEAKER ANGLE OF

INCIDENCES

10 °,

/.l AMPLIFIER ANGLE OF REFLECTED -

SOUND REFLECTION

Fig. 2

At A, incident and at B incident and reflected sound waves.

Fig. 3 I lustrating this manner in which a sound wave may be reflected by the walls, ceiling, and floor of a

room. Follow the arrows.

MOST really good contributions to knowledge cannot be car- ried to extremes, and oscillation, in one form or another,

is no exception to this commonly accepted axiom. Intentional regeneration in R.F. and, very often, in A.F. amplifiers has been one of the major steps in the development of radio; but, as stated above, becomes the most de- structive of forces when used in excess or when not wanted.

The subject of oscillation control in R.F. circuits has been treated so often and to such an extent that repetition would be boring; oscillation control in A.F. circuits has not been discussed to any appreciable length lately, so an attempt is made here to lay before the reader the causes, and what is far -

more important, the cures of audio oscillation.

Oseïlletion in the Amplifier There are two possible causes of

audio oscillation; (1) that due to improper design of the amplifier itself; and (2) that due to feedback from a loudspeaker to a microphone, both of which are connected to the audio amplifier in the conventional manner.

The first cause of oscillation may be cured only by electrical means, but the second cause may only be eliminated by mechanical methods, since the source of the trouble is due to the kinetic energy (energy due to motion) of the sound wave issuing from the speaker and entering the microphone. Each of these methods will be treated in detail, in turn.

In order for oscillation to take place, energy must be transferred from one portion of a circuit to another, without the aid of an external source of energy. In a vacuum tube, energy may be fed from the plate to the grid circuit either through the internal capacity of the tube itself or by means of external coils and condensers, and if the energy fed back is sufficient to overcome the losses in the grid circuit, the tube will generate self -sustained oscillations. The one requisite, however, is that the resistance of the circuit, R, must be less than 4LC, where L is the inductance and C is the capacity of the circuit. If R is greater than 4LC, there will be no self - sustained oscillations.


In an audio circuit, it is very un- likely that energy will be fed from the plate to the grid circuit via the tube capacity because of the relatively small internal capacity of the tube compared with the frequencies used; but it is possible that energy from one circuit (either the plate circuit of a tube, or the grid or plate circuit of another tube) may induce a voltage in a grid circuit, which will be amplified by the tube, fed back to the grid circuit again, etc., generating oscillations of a troublesome nature. Oscillations arising from such causes are due to interstage coupling.

The obvious remedy, of course, is to so place the individual units such as transformers, chokes, etc., so that the coefficient of coupling (degree of coupling) between any two coils is a minimum. The best position may easily be determined by connecting up the amplifier and adjusting the position of the various units until the oscillation ceases.

Another cause of oscillation is improper grounding of the amplifier and its associated units. If the potential of the grid- return is not held fixed but assumes any value determined by local conditions, the potential of the grid with respect to the cathode will fluctu- ate, resulting in oscillation. If the source of "B" potential is a power unit, then the variation in grid potential will take place at double the frequency of the power supply, i.e., 120 cycles, giving a decided hum.

"Motorboating" in resistance -coupled amplifiers is not an uncommon occur- rence, and is, in reality, a low -frequency oscillation. It is caused, in most cases, by the variation in voltage on the grid of a tube due to coupling through a common impedance. This point will be further discussed.

In transformer -coupled amplifier circuits, oscillation, if not due to improper placement of the components parts, is present because of coupling through a common impedance. The idea may be represented by Fig. lA. The plate current of tube V2 must flow through R1 and R2, through the tube, to the B -. The plate current of tube VI must flow through Rl, through the tube to the B -. The result is that, if


343



RADIO - CRAFT'S CHART OF

INTERMEDIATE FREQUENCIES MANY SERVICE MEN are laboring under the erroneous impression that 175 kc. is the "standard" intermediate fre-

quency used in present -day broadcast superheterodynes. So much publicity was given this particular frequency when the "super" returned to popular favor two seasons ago that they overlooked completely the great amount of development work done since that time. More than one repair man has vainly tried to line up supers at 175 kc. when

the actual working frequency was either higher or lower!

For the benefit of Service Men, we circularized all domestic radio manufacturers known to be in business, asking

them simply for the I. F. used in all supers that they now make or ever made. Phis list which follows represents the total response to date. If further ''dope'' is received, we will publish a similar list in the near future.

ALL -AMERICAN MOHAWK CORP.

Lyric models S -6, S -7, S -8, S -10, S -63, S -65, DC -65, B -80, S -80, SA -90, SA- 130 175 kc.

Lyric models SW -8, SW -80 484 kc.

ATWATER KENT MFG. CO.

Model 91 Auto Radio 260 kc. All other models 130 kc.

AUDIOLA RADIO CO.

All models 177.51m.

BALKEIT RADIO CO.

Models L7, 55, 85 175 kc.

BELMONT RADIO CORP.

5 tube models 51B, 51C and 55B; 7 tube models 71 and 71A; 8 tube model 81; 11 tube models 110 and 110A 175 kc.

BROWNING DRAKE RADIO CORP.

Models 40 and 80 175 kc.

CANADIAN WESTINGHOUSE CO., LTD.

Models 89, 90, 99, 99A, 110, 120 171 kc.

Columaires 8 and 10, and models 101, 801, 802 178 kc.

COLONIAL RADIO CORP.

All models 175 kc.

344

COLUMBIA PHONOGRAPH CO., INC.

C -25B chassis in C -256 receiver, C -55 chassis in C -53, C -54, C -59 receivers, C -80A chassis in C -81, C -83 receivers, C -80B chassis in C -84 receiver, C -90A chassis in C -93 receiver, C -90B chassis in C -94 receiver, C -120B chassis in C -123 receiver (battery), C -220 chassis in C -223 receiver, C -550 chassis in C -559 receiver, C -800A chassis in C -85 receiver; all 175 kc.

CROSLEY RADIO CORP.

Models 95, 96, 129, 130, 132 -1, 133, 134, 135, 137, 141 181.5 kc.

Models 120, 121, 122, 123, 124, 125, 126, 127, 128, 131 175 kc.

Model 136 -1 456 kc.

DE FOREST CROSLEY RADIO (A Division of Consolidated

Industries, Ltd.)

1931 Models: all Challenger models; Encore (500), Ballad (501), Carol (705A), Musicale (707A), Little Symphony (840), Rhapsody (850), Carillon (853), Clifton (405C), Canter- bury (405A), Chesterfield

(405B), Westmin- ster (405D -E -F), Westminster Uni- versal (607), Pre- lude (905), Belcan- to (907), DX -Plus (855B), Herald (855) ; 1932 Mod- els: Windsor (608A), Renwick (608C), York (851A), Mayfair (851C), Embassy (801), Battery Montrose (902), Balmoral (140) ;

All 175 kc.

DELCO APPLIANCE CORP.

32 volt D. C. Super- heterodyne 110 volt A. C. Super- heterodyne 175 kc.

RF 732 and 852; All 175 kc. (Note that besides the

model number there are letter designations. These appear after the serial number of the receiver and they help designate the type chassis. For instance, a receiver bearing serial number 0000 -RE will indicate that the chassis could be one from either a model 73 or a model 85.)

GENERAL ELECTRIC COMPANY

All models 175 k0.

GRIGSBY-GRUNOW CO.

All models 1 7 5 ke.

ECHOPHONE RADIO MFG. CO. LTD.

GULBRANSEN COMPANY

Models 130, 135, 235, 236, 237, 530,

Models 62, 72, 92....115 kc. 535, 925, 3225, S -5, S -5 Special, 5, 3226, 3925, 8726..175 kc.

10, 15, 20, 35, 50, Models 3521, 3525, 55, 60, 80, 90

65, 70, 75, 175 kc.

3622 262 kc.

EMERSON RADIO & PHONO- GRAPH CORP.

Model AW -55 Six tube Superheter- odyne 445 kc.

Models CS -52, JS -53, KS -70, KS -80 175 kc.

FADA RADIO & ELECTRIC CORP.

KU 45, KW 48 and 49, KO 51, KOC 53 and 57, KX 61 and 63, KY 66, RE 73 and 85, RC 78 and 79, RA 74, 76, 83, 87, 88 and 89,

RADIO -CRAFT

HAMMARLUND MFG. CO.

Comet All Wave Su- perheterodyne, Comet Pro, Models A and B 468 kc.

CHARLES HOODWIN CO.

6 tube Midget, 6 tube Auto set 175 kc.

All -Wave Chassis 456 kc.

HOWARD RADIO CO.

Letters indicate chassis model, numbers t h e corresponding cabinet

for DECEMBER, 1932



models. H(35, 40), A V H (4 5, 6 0), 0 (20, 25, 30), AVO (35A), DL (500, 5 0 1), K (400), L (4 2 0), M, EX 175 kc.

Automobile receivers 260 kc.

KELLER -FULLER MFG. CO. LTD.

Los Angeles, Cal Radiette Models 70, 80, 90, 120, and 50S 175 kc.

COLIN B. KENNEDY CORP.

Models 52, 56, 62, 62A, 62B, 63, 64, 64B, 66, 66A, 66B 72 175 kc.

Model 52 (export) - - 135 kc. Model 67 (export) -- - 110 kc.

KOLSTER RADIO, INC.

Models K -55, 60, 62, 63, 65, 66, 70, 72, 73, 75, 76, 80, 82, 83, 85, 86, 90, 92, 93, 95, 96, 100, 102, 103, 105, 106, 110, 112, 113, 114, 115, 120, 122, 123, 125, 130, 132, 133, 135, 140, 142, 143, 145, 165, 195 all 175 kc.

LANG RADIO CORP.

Models MA7, MD7, SA7, SD7, MA8, MD8, SA8, SD8, SA9 175 kc.

C. R. LEUTZ, INC.

Special short -w a v e receiver 450 kc.

LINCOLN RADIO CORP.

Deluxe SW -33, DC- SW10 480 kc.

PHILCO RADIO & TELEVISION CORP.

7 Philco Transitone. -175 kc. 15 Series 175 kc. 22, 23 Series 260 kc. 35 260 kc. 36 Series 260 kc. 47 DC Series 260 kc. 51, 52 Series 175 kc. 70 and 70 with auto-

matic volume control 260 kc.

71 Series 260 kc. 90 with 45's in out-

put, and 90 with one '47 in output 175 kc.

90 with two '47's in output 260 kc.

91 Series 260 kc. 111, 112 175 kc. 4 and 4C Series 3600 kc.

adjusting frequency

PILOT RADIO & TUBE CORP.

Dragon, models 10 and 11 115 kc.

Models 39, 41 115 kc. Models 148, 149 175 kc.

RCA -VICTOR CO., INC.

Radiolas 60, 62, 64, 66, and 67 180 kc.

All other RCA, RCA - Victor and Victor

Talking Machine receivers 175 kc.

REMLER CO., LTD.

Model 10 260 kc. Model 15 180 kc.

SILVER- MARSHALL, INC.

Models 36A, 41, 714, 716, 724, 724B, 726SW, 782 -1040, A, B, C, D -E, F, G, J 175 kc.

Models Q, QD, R -RT, V, X, Y 465 kc.

SIMPLEX RADIO CO.

Models P, P -DC, P- Battery, T (automobile) 175 kc.

SPARKS- WITHINGTON CO.

Models 10, 12, 14, 15, 16, 16AW, 18, 25, 26, 26ÁW, 27, 28, 30, 30A, 34, 35, 45 172.5 kc.

STROMBERG -CARLSON TELE- PHONE MFG. CO.

Models 19, 20, 22, 24, 25, 26, 27, 29, 38, 39, 40, 41 175 kc.

TRANSFORMER COMPANY OF AMERICA

Models 80, 81, 83, 84, 85, 86, 90, 91,

94, 95, 96, 100, 101, 110, 111, 120, 121, 130, 131, 160, 170, 220, 230, 260, 270, 280, 290 175 kc.

Models 140, 150 (short wave combination) : on short waves receiver is tuned to 600 kc.

Model 125 100 kc. Model 240 490 kc.

TRAV -LER RADIO & TELEVISION CORP.

Models S -9 and S- 10..175 kc.

UNITED AMERICAN BOSCH CORP.

Model 260 517.5 kc. All other models to

date 175 kc.

WELLS GARDNER, INC.

Series 052, 062, 072 262 kc.

Series 50, 022, 572, 092 175 kc.

ZENITH RADIO CORP.

Models AH, CH, RH, LH, WH, MH, BH..175 kc.

Models 090, 90, 91, 92, 103, 210, 220, 230, 240, 245, 410, 411, 420, 430, 440 175 kc.

Models 210 -5, 211 -5, 270 -5 125 kc.

Models 250, 260, 272 175 and 1000 kc.

"FERROCART" R. F. COILS

EUROPE, via the efforts of Hans Vogt, has recently become aware of the possibilities of the use of finely- divided iron as R.F. coil

core material, à la the general idea dis- closed in complete detail in the Novem- ber, 1931, issue of RAD10- CRAFT, in the article, "Permeability Tuning."

The main advantages of this material, when used as the core of an R.F. transformer, are low resistance losses and high permeability. This latter factor manifests itself as a coil of much smaller dimensions than that ordinarily used, as pictorially represented in the photograph attached. The larger unit to the left is a coil having identical electrical characteristics -but note the difference in size!

Another distinct advantage is the fact that the material may be com- pressed by the application of heat and pressure; and it may be stamped, cut and sawed to almost any desired shape.

DR. ALBERT NEUBURGER, Berlin

Selectivity curves of Ferrocart, in comparison with other coils having the same inductance, are distinctly steeper, indicating a lower R.F. resistance. At resonance, the response of a Ferrocart coil reaches 10 (arbitrary units). Un- der the same conditions, the usually efficient R.F. coil reaches 5.7, a ratio of 5.7/10 or .57. At 5 kc. off the measuring frequency, the Ferrocart coil as a response of 4.5 and the usual R.F. coil


a response of 3.5. The ratio at this point is 3.5/4.5 or .77.

The above ratios mean that at resonance the usual R.F. coil is but 57% as sensitive as a Ferrocart coil, and at 5 kc. off resonance, the usual R.F. coil is but 77 % as efficient. With these figures, a figure of merit of the coil may be obtained. The above data were taken from measurements made at 300 meters, or 1,500 kc.

The decrement of the coil at 200 meters is about .04 and drops to about .01 at 600 meters, which is to be expected. In comparison with another coil which had a decrement of .06 at 200 meters and a decrement of .035 at 600 meters, the Ferrocart coil is good.

In the article "Permeability Tuning" referred to above, tuning of the coil was accomplished by varying the amount of iron in the coil; in this coil, tuning is accomplished by a standard tuning condenser.

313



G(ID CLIP NQ .2

GIN. LEAD

I CONNECT FO R 57, 58 ANALYSIS

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346

C O N S T R U C T I N G

ADAPTERS FOR F. L. SPRAYBERRY*

WHY YOU SHOULD USE ADAPTERS

THOUSANDS upon thousands of tube testers and se+ analyzers have been sold to Service Men prior to the announcement of the six- and seven -prong tubes. To discard such instruments, merely because they do not test some of the latest tubes, is unwise from both an economical and technical standpoint. For this reason, RADIO -CRAFT has printed in the October and November issues diagrams and descriptions of adapters suitable for testing all the latest tubes. When the series is completed, adapters designed for all of the well -known makes of testers will be described.

THIS is the third of a series of articles by Mr. Sprayberry dealing with the use of Na -Ald adapters for modernizing old test equip-

ment. In the October and November issues of this magazine adapters suitable for use with Jewell analyzers were discussed; in this issue, we proceed with a discussion of adapters for use with Weston and Supreme apparatus.

Adapters for Weston Testers

No. 932, Fig. 5, is used with the model 537 tester to analyze the '22, '32 and '34 tube circuits.

No. 992, Fig. 6, is used with the model 537 tester to anlyze the '24, '35, '36, '38, '39, 44 and '51 tube circuits.

No. 965DD, Fig. 63, is used with the model 537 tester to analyze the circuits of the 29, 41, 42, 55, 57, 58, 69, 85, 89, PA, PZH and 6 -prong Wunder - lich tubes making possible the measurement of plate current, plate voltage and control -grid bias.

Service Consultant. National Radio Institute.

No. 955DGLC, Fig. 45, makes possible the direct analysis of the 1st section of the triple -twin tubes with the model 537 analyzer.

No. 955DPP, Fig. 46, is used with models 547, 565, 566, 589, 593, and 660 testers for direct analysis of the 1st section of the triple -twin tubes.

No. 954DP, Fig. 64, is used with models 537, 547, 565, 566, 589, 593 and 660 testers for direct analysis of the 2nd section of the triple -twin tubes.

No. 955GGKC, Fig. 47, is used with all models of Weston analyzers to secure direct analysis of the 5 -prong Wunderlich tube circuits. This adapter is used on the 5 -prong analyzer plug or the 5-prong adapter of a 4 -prong analyzer plug.

No. 955GGKL, Fig. 48, is used in the 5 -prong analyzer socket in conjunction with the No. 955GGKC adapter for 5 -prong Wunderlich tube analysis.

No. 975DD, Fig. 49, is a twin adapter to be used with the model 537 tester for analysis of 7 -prong tube circuits enabling plate current and voltage, filament voltage and grid -bias readings to be taken.

No. 975DW, Fig. 50, is a twin adapter for use with models 547, 565, 566, 589 and 593 testers to analyze the circuits of the 7 -prong tube. This adapter enables plate voltage, screen - grid voltage, control -grid voltage, filament voltage, cathode voltage, plate current and screen current readings to be taken.

No. 975DSW, Fig. 51, is like the No. 975DW excepting that it has a center stud for locking into the latch of the analyzer plug of the model 565 tester, Typi.+5.

No. 967SGL, Fig. 65, is used on the

70 FIG. 71

F- F+

FIG. 72

rci PHONE

TIP JACKS

F- F+

FIG. 73

Schematic circuit of Figs. 63 to 73 inclusive. For other figures referred to in the article, see past issues of this magazine.




This third article by Mr. Sprayberry describes in detail adapters for use with Weston and Supreme apparatus.

TEST EQUIPMENT

6 -prong analyzer plug of the model 660 tester, and the No. 976GL, Fig. 66, is used in the 6 -prong socket of the tester for analyzing 7 -prong tube circuits.

No. 968R, Fig. 54, is used with Weston models 533, 555. 565, 593 and 597 testers to check the WD11 tube in the '26 socket.

No. 944R1, Fig. 55, is used with the above Weston models for checking the 864 tube in the '26 socket.

No. 972R1, Fig. 56, is used with the above Weston models for checking the 215A tube in the '26 socket.

No. 944GL, Fig. 62, is used with the Weston model 565 tester for analyzing '32 and '34 tubes.

No. 954KPC, Fig. 15, is used with Weston models 533, 555, 565 and 593 testers for checking '33, 46, '47, GA, LA and PZ tubes.

No. 955GGKL, Fig. 48, is used in any Weston tube checker to test the Wunderlich 5 -prong tube. Place in '27 socket.

No. 965GG, Fig. 28, checks the 29 and Wunderlich 6 -prong "A" tube in the '27 socket; and the 69 and Wunderlich "B" tube in the '27 socket with 6.3 V. heater voltage of any Weston tube checker.

No. 965 -55, Fig. 26, is used with all models of Weston testers for checking the 55 tube in the '27 socket. This adapter also checks the 85 tube when placed in the '37 socket or when 6.3 volts is applied to the heater terminals of the '27 socket.

No. 965KPGL, Fig. 67, is used with Weston models 533 and 565 testers for checking the 57 and 58 tubes in the '27 socket.

No. 944LS, Fig. 44, is used with the Weston model 597 testers for checking the overhead heater tubes.

No. 429, Fig. 40, is used with all models of Weston testers for checking UV199 tubes.

No. 944GL, Fig. 62, is used with models 533, 555, 565 and 593 testers for checking the '22 tubes. This adapter also checks the 865 tube in the model 597 tester.

No. 979WE, Fig. 57, is used with models 533, 555, 565 and 593 testers for checking the Western Electric 205D tube. This adapter may be used with a No. 954 adapter to check the 205D tube with the Weston Model 597 checker.

No. 954KPC, Fig. 15, is used with the model 597 tester to check the GA tube.

No. 954SGL, Fig. 68, is used with the Weston model 565 tester to check the '36, '38, '39, 44, '64, '65 and 68 tubes.

No. 965PG, Fig. 25, is used with models 533 and 565 testers for checking the 41, 42, PZ and PZH tubes.

No. 965KS, Fig. 16, also checks the 89 tube in models 555, 593 and 597.

No. 965KPGL, Fig. 67, checks the 89 tube in models 533 and 565 testers.

No. 975KP, Fig. 35, checks the new 7 -prong power amplifier with any Weston tube tester.

No. 954GL, Fig. 53, is for testing the circuits of pentode tubes with models 547, 565 and 566 testers. It is to be placed in socket of tester.

No. 945GL, Fig. 52, same as for the No. 954GL with the exception that it is attached to the test plug.

No. 954DS, Fig. 20, is used with models 565 -5 and 566 -3 testers.

No. 965DW, Fig. 8, is used with the model 565 -5 tester for test on 57 and 58 tube circuits.


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Diagrams of adapters for Figs. 74 to 84 inclusive. In issues to follow, adapters suitable for additional testers will be given.




THE SERVICE MAN'S FORUM Where His Findings May Benefit Other Radio Technicians

WHEN THE SET'S "ALL WET" - PAGE MR. GIBBONS!

Editor, RADIO- CRAFT:

I read with interest, in RADio- CRAFT, the different experiences of Service Men throughout the country. Now, I am prompted to submit to the readers the following rather interesting experience.

One of my customers recently purchased a battery- operated Eagle radio set which would not operate. After testing the circuits and carefully going over the receiver I found that dampness had got into one of the audio transformers. This moisture then was absorbed by the paper wrapping and, ex- panding, had broken one of the hair- like strands of the secondary.

After putting in a new transformer and carefully drying out the set by putting lighted electric lamps in it near the coils, we hooked it up and it played and sounded as good as when new. Luckily, the man who owned the set heard it play in our lab., while we were testing it.

He took the set home, fully satisfied that it was going to play and that we had done a good job (which we felt we had) -but Ah- h -h -h! He dropped into the place the next day and Oh! Boy - was he mad! He told us we had charged him to fix his radio and it wouldn't play -and were we surprised!

I first contended that he must have hooked it up wrong so, to compromise with him and to keep customer good- will, without losing any money, I agreed to go to his home, about seven miles away, for traveling expenses only, if it was the fault of our work- manship. On the other hand, he agreed to pay us for my time and expenses if the fault was his.

Upon arriving at his home I noted that the set was in a room directly over a basement. Next, I turned on the receiver, the side -tone was normal and a buzz resulted when I touched the grid connection of the detector -audio end, O. K.

What? The coils look damp again? Sure enough; damp enough so that a mark is left by touching them. Well, after a little quizzing, the customer ad- mitted that the room was damp, and also that the same trouble developed at his brother's house, even with a cook stove burning.

Consequently, I decided to take the set back to the shop, dry out the R. F. coils so that the set would play, and then leave the set in the shop over night, as I was sure there was no dampness in our place (heating engineers had previously tested for dampness before installing an oil furnace).

348

e firs sign o . urn, it continues.

0000000000000100000000 Ó

O GIBBON'S ó O

RADIO COLUMN O

O Radio Questions answered p in this column every week. 0

O

8

pFree! O

Send in your troubles. Ad-

Hdress Radio Editor, in care

p of this paper. 0 woCDon THE D.X.ers GLORY.

How do you do friends .of the air. Happened to be at a

tó*n called Westbrookville. N. Y. recently and became acquainted with a chap who is a short wave fan so went to his home and to our, .

surprise heard Madrid, Spain with! enough volume for loud speaker reception and held the program pi for the entire supper hour. I was O so completely bewildered I didn't leave the speaker. Several other European stations were heard and with volume and a new thrill has been -added to our radio advent-, ures. So far I believ we've found the best spot in this section of the world as far as D,X. reception is concerned as the best-set in the world depends upon the location in which it is used.

ou es it C.

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f. v. a lo c. f'

QUESTIONS AND ANSWERS Q- Please give -me the address

of Philco as my socket power has a burned out fuse on the Det. tap and I want a new one. T.B. Milford

A- Address is Philadelphia, Pa. The Det, tap has no fuse on it as it is a fixed 'resistance of 100,000 ohms.

A Q- Does a radio work as well .i

plugged in the lamp socket as it

ò would in a receptacle or floor plug It is á Sparton Type 89A? B.NJ. Goshen, N.Y.

A- It will work in the lamp socket but the plug is the best as a lamp cord offers more resistance than the plug thereby cutting down the current supply to the set,

Meet me here next week. JOE GIBBONS

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Mr. Gibbon's column. He "takes the resistance out of radio."

Next morning, when I. came to work I noticed that the coils were again damp and that the set would not play! Believe me, I sure was puzzled, so I decided to follow up one more hunch.

I went to the drug store and got some blue litmus paper. Returning to the shop, I touched the coils with the litmus paper; it turned pink, indicating an acid condition which was causing the coils to absorb moisture, no matter how many times they were dried out.

The first step was to neutralize the acid, which I did by soaking the coils overnight in ammonia. After drying out the coils by placing them close to a bank of lighted electric light bulbs I coated the coils with pure orange shel- lac.

The set has been playing now for five months and the customer is so well pleased he has sent us plenty of other customers.

In several subsequent cases we have found this same "dampness trouble" affecting the battery set, especially where the set is installed directly over the storage "A" battery, as the fumes of the acid seem to creep into the coils. It is my belief that this trouble is causing a loss of volume, or "kick," in battery sets. Now, our motto regarding a battery set powered by a storage "A" or "B" battery is, "Keep the battery away from the set."

Hope this information helps out the bunch.

Jon E. GIBBONS, Pioneer Radio Laboratories, 16 Holden

Building, Port Jervis, N. Y. (We thank the Pioneer Radio and

Detective Laboratories for this tale of a job well done. There is no better recommendation than the customer who comes back for more. Editor)

THE Official Radio Service Men's Asso- ciation, sponsored by RADIO -CRAFT,

invites all Service Men who are not members of the Organization to write for an application blank. It is the official service organization of this magazine and is main-

Official lapel button of the O. R. S. M. A.

tamed solely for the interests of Service Men. Membership cards are issued upon passing a written examination which is forwarded by mail. Write for yours today. The O.R.S.M.A., 98 Park Place, N. Y.




r

THE ANALYSIS OF RADIO RECEIVER SYMPTOMS

OPERATING NOTES COLONIAL 33 RESISTORS

Oscar Block

IN THE Colonial 33 series and in other sets using lavite, graphited, or similar voltage- divider resistors, a frequent cause for either low plate- or

screen -grid voltage, high control -grid bias, or grid blocking is the rise of the resistor's value due to its element dis- integrating in operation or its contacts becoming imperfect.

The simplest procedure to follow in effecting a cure where the desired resistance values are in doubt is to connect a high resistance voltmeter across the tube and to shunt the voltage divider sections with small, carbon, pig- tailed resistors of sufficient current - carrying capacity until the proper voltages have been obtained. It is well to check all the voltages again after tentative resistance values have been selected, as a change of resistance in one section is apt to change the voltages across all sections. This cure is preferable to changing any resistor whose value has changed, since unless a complete open is encountered, the parallel resistors will have a greater current -carrying capacity. This idea is shown in Fig. 1.

APEX No. IO

By Adolph Kohnert

STATIC and noise was the complaint on an Apex No. 10, brought into the

shop for repairs after all efforts failed to fix the set in the field. Tests revealed that the noise, sounding like a noisy tube, was due to an 8 mf., dry electrolytic, paper case condenser which bypasses the detector plate feed resistor. This trouble occurred in several sets of this model, and was eliminated by replacement of the condenser.

BOSCH 73

A peculiar trouble was had with a Bosch 73. The customer reported "something burned." The set was turned on and found to be in playing order. The chassis was removed from the cabinet and a black, with yellow -tip resistor was found to be burned. This resistor has a value of 5,000 ohms and feeds the plate of the second R.F. screen -grid tube. All associated circuits and parts were checked and found O.K.; so were all tubes. At last, the customer was questioned regarding the set. He revealed that he had the tubes tested and switched the tubes around and in so doing inserted a '27 tube in a '24 tube socket, but corrected this before the Service Man got there. When the '27 tube was put in a '24 tube socket, the tube was drawing 40 ma. (plate current) due to the applied screen -grid

WHAT THIS DEPARTMENT IS FOR

It is conducted especially for the professional Service Man. In it will be found the most unusual troubles encountered in radio service work, written, in a practical manner, by Service Men for you.

Have you, as a professional man, encountered any ""nusual or interesting Service Kinks that may help your fellow workers? If so, let us have them. They will be paid for, upon publication, at regular space rates.

TO -e+ MAX.

s X SHUNT

RESISTAN. CES

N. // VOLTAGE MEASURING

POINTS

TO a= 'MAX'

MAIN VOLTAGE DIVIDER

Fig. I

Connections for the pig -tail resistors.

15,000

' OET. ,RFC. j.5-MF, ssss

6 0.1-MEG

Jr.

OHMS 55,0po 014M$

440 OHMS'

.... MERSNON iltk e e-e

ELECTROLYTIC

Fig. 2

Insertion of the 15,000 -ohm resistor improves recep Lion in this receiver.

Fig. 3

Chassis layout, showing where to find the part

RADIO -CRAFT for DECEMBER. 1932

volts being on the control grid. This again shows how important it is to question the customer regarding his set.

On another of the same model, the set was playing with low volume when first turned on, but would, in about ten minutes, suddenly play normally. This trouble was caused by an open third R.F. screen -grid resistor. This is a 750 -ohm, flat, wire -wound resistor. It was replaced by a 1. watt carbon type.

CROSLEY MODELS 30S, 31S, 33S AND 345 RECEIVERS

Henley M. Hilburn

THERE are a large number of Crosley models 30S, 31S, 33S and 34S re-

ceivers in use at present that are reaching the age that calls for frequent servicing. Naturally, new tubes, re- alignment, and perhaps the addition of a few new plate- circuit resistors usually make the set as good as new.

However, if the Service Man will add a 15,000 -ohm resistor between the positive side of the 55,000 -ohm detector plate resistor and ground, he will be surprised and the customer delighted at the increase in volume and tone quality.

The location of this resistor is shown in the sketch of Fig. 2.

SPARTON RECEIVERS Arthur B. Parker

IN all the Sparten receivers with the R.F. amplifier in one can, there is a

plate bypass condenser that blows quite often. To make replacement easier and quicker, I have used the following method.

Refer to Fig. 3, a chassis layout of the set. Remove the screw "Sl," and from its lug solder a wire to one plate of the new bypass condenser to be installed. The other wire from the condenser solders to the lug marked "S2." A pig -tail type condenser makes a very neat job, and it is not necessary to remove the unit from the cabinet.

APEX MODEL 36 M. R. Cooper

AN Apex 36 receiver that had been giving good service suddenly de-

veloped a queer habit of dying out with a p- l -o -p; this happening after about 30 to 40 minutes of operation. The owner who noted that the tubes were all lighted turned the set off. Perhaps 15 minutes later it was turned on again but functioned in exactly the same manner as before. The set was sent back to the company from whom it was purchased, who maintain a so called


349



79 Radio Service Data Sheet

BOSCH "VIBRO- POWER" TRIPLE -ACTION MODEL 312 I2 -TUBE

"GRAND OPERA" SUPERHETERODYNE

(Dual reproducers, inter -station noise cutout, A.V.C., tone control, push -push power amplification, local -noise con-

trol, tuning meter, antenna compensator, hum control, mercury -vapor rectifier, band selectors, low -drain tubes.)

The term "Vibro- Power" undoubtedly has puzzled many persons who may have come in contact with this generalization of Bosch. The term refers to the Bosch receiver ensembles which incorporate the features enumerated above.

Triple action is obtained in the A.V.C. circuit as follows: Reduction of station noise by the application of time -delay operation ; complete elimination of inter- station noise by adjustment of an auxiliary tube circuit, and; equal anti -fading or automatic volume control operation over the entire tuning band.

Following are the characteristics of the components: Resistor Rl, manual volume control, 0.5 -meg.; R2, tone control, 0.1 -meg.; R3 hum control, 20 ohms; R22, "individual -location" noise control, 2.000 ohms; R4. R5, R17, R26, 0.1 -meg.; R6, 500 ohms; R7. 0.5 -meg.: 118.

RIO, R11, R13. 1.0 meg. ; 119, 2 megs. ; R12, R19, 1121, 1,000 ohms: 1114. RI6, R16, R29, 10,000 ohms; 1118. 1.500 ohms; 1120, 30,000 ohms ; 1123, 2.800 ohms ; 1124, 2,400 ohms ; 1125,

R27, 5.000 ohms; 1128. 4 ohms; 1130, 3,000 ohms. Condensers CI to C4, tuning units CIA

antenna compensator and R.F. trimmer, C2A to C4A R.F. trimmers: C5 to C9. I.F. trimmers: C10. oscillator padding condenser; C11, C12. 0.1 -mf.: C12, C14 to C22, C24 to C26, C80, C31, C37. C39, .05-mf.; C23. C36, C38, 100 mmf.; C27, 0.5-mf.; C28, C42, C43. 8 mf.; C29. C33, C34. C85, C41, 4 mf.; C82, .06 -mf.; C40. C46, .01-mf.; C44, 2 mf.

Tube operating voltages (except filament). measured to ground, are as follows: Filament potential, all tubes, 2.4 V. Plate potential. VI, V2, 180 V.; V3, 75 V.; V4, V5, 195 V.: V6, 0.0 V.; V7, 120 V.; VS, 290 V.; V9. VIO, 430 V.; VII, 2 V. Control -grid potential, except V8, 0.0 V.; V8. 30 V. Screen -grid potential. VI, 85 V.; V2, V4, VS. 90 V.; V6, 2 V.; V7, 25 V.; V7. 1.0 V.; V.8. 290 V.; V9. V10. 0.0 V.; V11. 25 V. Cathode potential, VI, 3 to 6; V2. 4.5 to 10 V.; V4, V6, 3.5 to 6 V.; VS, 40 V.; V7, 45 V.; V11, 0 to 46 V.

Tuning meter M operates over a range of 0 to 16 ma. The receiver consumes 80 to 150 watts, depending upon the A.F. volume;

.NT r CIy1 I ci T 1

CS

CIL i r "T I Ì 0.1 IFTI

the Underwriters Laboratory rating (12% above minimum current drain) would be 90

watts. The sensitivity of the Bosch model 312 receiver is 1 to 2 microvolts absolute, at a

power output of 100 milliwatts. The A. F. response characteristics of the two reproducers (one model C and one model G) are nearly identical; each field coil has a resistance of 2,600 ohms. The recommended antenna length is 40 to 80 ft. At the front left of the chassis is the combination off-on switch and manual volume control Rl ; in the center, the tone control, 112; and right, tuning control; condenser CIA is located in back of the tuning control. The "individual location" control (on the side of the cabinet) varies the proportion of program background noise; sensitivity above the noise level is not affected. The triple -diode second -detector is so de-

signated since it acts as three diodes, as follows.

The modulated I. F. output of the T. F. amplifier is applied to the control -grid and cathode of V6; the A. F. or'wut is developed across Rl and applied to t .e control -grid of V7 ; this disposes of one diode. The modulated I. F. output of the I. F. amplifier is also applied to the plate (to which also is tied the suppressor -grid) and cathode of V6: the

A.V.C. potential is developed across R8 and applied to the control -grids of V1, V2, V4 and V5 only when this potential exceeds the control -grid potential of 40 volts (the D.C. drop across the total resistance of 1122. one end of which connects to the secondary of I. F. T. 3) ;

this disposes of the second diode. The modulated I. F. output of the I. F. amplifier at the same time is applied to the screen -grid and cathode of V6; the inter -station noise suppressor potential is developed across RO and applied to the control -grid of Vil only when this potential exceeds a pre-determined screen -

grid potential between 0 and 40 Volts (the D. C. drop across the portion of 1122 between the ground end and the moving arm) ; this dis - poses of the third diode.

When there is no incoming signal, tube VII has screen -grid potential, plate potential, and

no control -grid potential. The plate therefore draws current and causes a drop across resistor 1111 ; this potential is applied to the control - grid of V7, biasing it to plate current cut -off.

When there is an incoming signal the screen - grid of V6 draws current and the drop across R9 is applied to the control -grid of Vll, biasing it to plate current cutoff, thus re- establish- ing the normal control -grid bias of V7. This action is assisted by the D. C. in Rl and to some extent reduces the screen -grid potential of V6 and Vil.

Note that while making adjustments on the chassis the service oscillator signal should not be permitted to overload the tubes, as this will result in incorrect settings.

To make adustments of the I. F. portion of the set, adjust RI to maximum, set 112 on treble. and ground the antenna lead. Then. connect the 175 kc. service oscillator to the control -grid of V2, and align CO for maximum output. Next. rig up an alignment "loner" consisting of a 25,000 ohm resistor and a 260 mmf. fixed condenser, and ground one of the two leads: the other end is to be connected either to the grid or the plate circuit of a

tube, as directed. With the free terminal of the losser connected to the control -grid of V5, adjust C7: then. with the loner connected to the plate of V4. adjust CS. Finally, connect the loner to the control -grid of V4, and adjust C5; then. with the loner connected to the plate of V2, adjust C6.

To align the oscillator circuits, adjust trimmer C4A for maximum output (with the set pointer past 550 kc.) from a 1,400 kc. service oscillator connected to the control -grid of V2. Note that when adjusting C4A two peaks may be obtained; after tightening the C4A adjusting screw. release it about 142 -turn until the peak at 1,575 kc. is obtained (otherwise the oscillator will not track in the center of the scale) ; then, align CIA, C2A and CIA. Finally, set the service oscillator for 600

kc. and adjust padding condenser CIO.

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350 RADIO -CRAFT for DECEMBER, 1932



Radio Service Data Sheet 80

SPARTON "TRIOLIAN" I 3-TUBE MODEL 28 3- SPEAKER SUPERHETERODYNE (Inter- station noise suppressor, parallel push -pull pentodes, duo -diode detector with twin 56's, line -noise filter,

tone control, hum control, Lafoy delayed A. V. C., parallel '80's, R. F. and I. F. band -selectors.)

Service Men will find after studying the schematic diagram of the new Sparton "Trio - Iian" 3- speaker superheterodyne that although at first glance the circuit arrangement is apparently quite simple. there is incorporated in the ensemble a multiplicity of operations which make it essential for each component to have exactly its rated value, consequently, no tolerance from the specified values should be permitted when making replacements.

The Lafoy system of delayed A. V. C. discussed in Lugo-CRAFT Data Sheet No. 70, July 1932, page 37, in connection with the Sparton model 40 receiver. is incorporated in the Sparton model 28 superheterodyne. The sensitivity of the set is 4 microvolts absolute, across the broadcast band, with an undistorted power output of 20 watts. The combination first -detector and oscillator, V2, in addition to performing these functions also has a gain figure of 40 to 1.

Following are the values of the components: Resistor Rl, manual volume control, 10,000 ohms; R2, tone control, 0.1 -meg.; R3, inter - station noise control, 9 mess.; R4, 3,000 ohms; R5, 8,000 ohms: R6, R7, 15 ohms; RS, RIO. 0.25 -meg. ; R9, R14, 0.5-meg.; R11, 0.75 -meg. ;

R12, R13, 0.1 -meg. Chokes RFC2 and RFC3 are 16 mhy.

Condensers Cl to C4, tuning units; CIA, antenna compensator and R. F. trimmer; C2A, C3A, C4A, R. F. trimmers; C5, .002 -mf.; C6, to C9, I. F. trimmers: C10, 60 mmf.; Cil, C12. C13, C27, C28, C30. 0.2-mf.; C14. C16, C17, 250 mmf.; C15. C26. .01 -mf.; C18, .002 - mt. ; C19. .05-mf.; C20, C21. .006-mf.; C22, 4 mf.: C23, C24, C25, 6mf.; C29, 0.5 -mf.

Transformer Tl has a step -down ratio of .7 to 1. for improved quality.

The three reproducers are pitched to reproduce low notes without accentuation. A 9 in. dynamic reproducer, resonant at 80 cycles, is used in the front grille, and a 7 in. dynamic reproducer, resonant at 130 cycles, in either side grille. It has been found that

BAND SELECTOR

'ANT ;1 T q F l EIA I

58 I IN" L & 060

'24

by positioning these two reproducers at an angle, a "three dimension" sound effect is obtained; that is, one experiences a sensation of depth when listening to the reproduction. Choke Ch. 1, 3,700 (left) and 2,400 ohms: Ch. 2. 260 (left) and 140 ohms; Ch. 3. 3.160 ohms, center -tapped; Ch. 4, 75 ohms.

The station selector of the model 28 set is directly below the illuminated dial; below this knob is another which operates the inter - station noise suppressor, R3. At the right of the latter control is another which adjusts the tone control, R2; and at the left, the combination power switch Sw. and manual volume control R1.

Resistor R3, which controls the inter- station sensitivity of the receiver. is operated as follows: Turn Rl full on; then. tune between the station wanted and an adjacent station, and bring in the undesired between- station noise; next, rotate the R3 control knob counter -clockwise until this noise is reduced to a satisfactory level, or until it disappears entirely; now. tune in the desired program and operate RI to raise or lower the volume as required. When tuning for distant stations, or if use of R3 is not desired, rotate the control knob of R3 clockwise as far as it will go. However, for reception of local stations this control may be used as a manual volume control, and when operated in this manner the control knob of RI should be turned to the full position; this eliminates the A.V.C. feature and permits the received signals to fade out and in if atmospheric conditions permit.

To adjust antenna equalizer CIA, tune in a weak station between 1,400 and 1,500 kc., and turn the volume control on full ; then, adjust CIA (by means of a hex -socket wrench) for maximum output. Adjust CIA only when the aerial circuit is changed. The recommended antenna length is 50 to 100 ft., and height, 26 to 60 ft.

It is preferable to use as a replacement for V2 a tube of similar characteristics. so that

IFT1

li

W0 -DIODE t F T 2 DOT 2, 2.56'

the dial kc. readings for stations above 1,200 kc. are not altered. If the tuning dial goes off- scale, adjust trimmer C4A before any others, at 1,400, 900 and 600 kc., as required.

Before adjusting the oscillator, R.F. or I.F. circuits. set Rl full on, R2 full left ( natural tone). and R3 full clockwise. It is preferable to use a crystal -controlled, A.F. modulated 172.5 kc. oscillator; its broadcast harmonics will be: 690, 862.5. 1,036, 1,207.5, 1,380, and 1,552.5 kc.

Two peaks will be noted within a one -half or three- quarter turn adjustment of trimmer C3A ; the correct peak is obtained with the down adjustment (capacity increase). Un- less the latter setting is obtained, tuning dead spots will occur at 1,300 and 1,450 kc., together with poor sensitivity at 900 and 600 kc.

To maintain the A.V.C. inactive, (that is, to prevent the action of the A.V.C. from keeping the signal at one level), in order to obtain accurate condenser adjustments, set RI to full on and R3 counter -clockwise.

Symptoms and remedies: Dial calibration incorrect; align oscillator. Weak reception, multiple peaks within a 40 kc. band from a loud local station, or hiss; align preselector circuits. When replacing an I.F. condenser or transformer. or when these circuits are out of alignment; align I.F. circuits.

Following are the Sparton model 28 tube average operating characteristics, with a line potential of 115 V. and RI full on: Filament potential, VI to VII, 2.4 V. ; V12, V13, 4.4 V. Control -grid potential, Vl, V3. 2.4 V.; V2, 7 V.; V4. V5, (1) ; V6, 9 V.; V7 to VIO, 25 V. ; VII, 65 V. Screen -grid potential. VI to V3, 94 V.; V7 to VIO, 296 V. Plate potential. Vl, to V3, 173 V.; V4, V5, (): V6, 9 V.; V7 to V10, 285 V.; V11, 40 V.; V12, V13. 348 V. Plate current. VI, V3, 6.5 ma. ; V2, 1.1 ma.; V4. V5. (1 1 ; V6. 6.6 ma.; V7 to VIO, 26 ma.; VII, zero; V12, 1113, 39 ma. (per plate). () A potential is present only when a signal is applied.

RFC2 A

56

DOUBLE OUSN- PULL A.F2 4.'47'5

CI C2 C2A CO

(L1

vs

X Y, CID

TONE CONTROL

R2 '. 0.FCI

foe

COIL

CII CAA R9

C13

(14 V9

Y Y

110 V A FIELD

COIL

LINE

SUPPRESSORS

DT

l`

f

Cil //120v

5 AMA. FUSE

R.FC.3 56 AvC.

{

Z \

R3 INTERiTATION

NOISE CONTROL

V11

MANUAL VOLUME CONTROL

R1,

X X

CO

-GND.

R6y ;1; HUM X CONTRO

C26

R8 COILS

RII

VIO

Y Y VOICE / COILS

HUM -BUCK COIL

RIO

C3D


CHASSIS /

C27

DIAL LIGHT

X X

-C28 I 172.5 KC.

351



Fig. A Photograph of the Analyzer Adapter unit.

Fig. I

Complete schematic circuit of the Analyzer Adap ter unit.

-A-

1

6'i2" IIL

METAL

TO HOLD COVER

14 TUBES i / PARTITIONS

TOOLS

121/3" Ir WALL ALL PARTS

II

METAL pONTS

TO HOLD

' (OVER I

WOOD LEDGES FOR COVER TO REST ON

METAL COVER FITS BETWEEN POINTS TO METAL POINT ANO

HOLD W000 LEDGES / WOOD LEDGES FOR f)'

-B- COVER TO REST ON

4

GROOVE FOR LATCH

PARTITION r CATCH

COVER OF METAL O

OR WOOD FRROM SOLDERING

C- BOLT-7 LUG

Fig. 2

Dividing up the suit case for use as a tool ki .

POSITIVE HIGH

VOLTAGE

D.PST SW

PILOT 4 -PRONG CUSHION SOCKET

UX TUBE BASE

000BLE GRID LEAN

MOUNT

SIX WIRE ''ABLE

TROUBLE LIGHT

Fig. 3

Use this idea for testing rectifier tubes.

352

SHORT CUTS IN RADIO SERVICE

$10 for Prize Service

Wrinkles

Previous experience has indicated that many Service Men, during their daily work, have run across some very excellent Wrinkles, which would be of great interest to their fellow Service Men.

As an incentive toward obtaining information of this type, RADIO -CRAFT will pay $10.00 to the Service Man submitting the best all - around Radio Service Wrinkle each month. All checks are mailed upon publication.

The judges are the editors of RADIO- CRAFT, and their decisions are final. No unused manu- scripts can be returned.

Follow these simple rules: Write, or preferably type, on one side of the sheet, giving a clear description of the best Radio Service Wrinkle you know of. Simple sketches in free- hand are satisfactory, as long as they explain the idea. You may send in as many Wrinkles as you please. Everyone is eligible for the prize except employees of RADIO -CRAFT and their families.

The contest closes the 15th of every month, by which time all the Wrinkles most be received for the next month.

Send all contributions to the Editor, Service Wrinkles, c -o RADIO -CRAFT, 98 Park Place, New York City.

The analyzer plug in Fig. A is used with one of three adapters. Associ- ated with the sockets are pin jacks for measuring the voltage between socket terminals; current measurements are made by means of plug -in jacks and the phone plug. The tip jacks also serve as a convenient means of making circuit resistance measurements between the tube elements and ground, with the receiver current off.

Clean all solder joints with alcohol. A feature of the adapter plug used is that the wire connecting to the screen - grid cap stud is also connected to the latch; when testing seven -prong tubes, the control grid lead is brought out to the latch stud.

List of Parts

One Na -Ald 6 -prong plug with 3

foot, 7 wire cable, type 906 WLC; Three Na -Ald adapters, one each of

types 964 -DS, 965 -DS and 967 -SS; Four Na -Ald mounting sockets, one

each of 4 -, 5 -, 6 -, and 7-prong type; Seven RTCo. insulated -top phone -

tip jacks; Five Try -Mo single -closed- circuit

,jacks; One Try -Mo bakelite panel, 3 x 10

x 1/2-in.; One Try -Mo carrying case, 3 x 10

x 4 in. inside dimensions.

Prize Award AN ANALYZER ADAPTER UNIT

Solomon Perlman, E.E.

SERVICE Men will welcome the analyzer adapter unit illustrated in Fig.

A; its circuit of connections is clearly indicated in Fig. 1. This device brings the Service Man's analyzer right up- to -date for the analysis of the modern five -, six- and seven -prong tubes.

MOUNTING NOLES BAKELITE PANEL, I/4" IN BAKELITE SPIDER I BRASS

FOUNDATION BLOCK / CONTACTS

TAPPED BAKELITE BLOCK

STEEL SPRING

COLLAR, ' BAKELITE / STOP

BRASS QUADRANT IVETED THROUGH

ITE CONNECTIONS SOLDERED TO SAME

OR CONNECTION.

OLD JACK FERRULES

L SHAFT ti

\s

4

i

SPRING COPPER CO ACT SHOES RIVETED TO BAKELITE SPIDER.SHORT QUADRANTS

TO CONTACTS THUS NO PIGTAILS

Fig. 4

This multi- switch was designed to replace the bu tons in the RADIO -CRAFT analyzer.

AN INEXPENSIVE TUBE AND TOOL KIT Harry Schmidt

THE writer solved the problem of obtaining an inexpensive and suitable

tool kit by adapting an "overnight" bag in a manner illustrated in Fig. 2. The one used by the writer holds four- teen tubes, soldering iron, resistors, and a number of small parts.

The procedure is to rip the lining from an overnight bag measuring about 18 x 11 x 51/2 ins., and then to paint the inside black. Make two thin wood partitions as shown at A and B

in Fig. 2; wooden ledges are required as rests for the compartment covers, which are made of wood or metal. A catch may be made from a soldering lug as shown at C; it pivots freely and catches in a small groove in the partitions. The metal points to hold the cover are small brads driven into the side of the bag and then cut off so that ?!A -in. projects and holds the cover.


RADIO-C RAFT for DECEMBER, 1932



Photograph of the new Lafayette amplifier, the circuit diagram of which is shown below.

57 46 APPROX. 2:1. DOwN

OUTPUT 'SOHNS `TRANS. Ì

0.5- 4.700 MEG. OHMS

.5 -WATT 20 WATT

I MEG

.25MF

J

EXTRA FIL. MAY BE TAKEN FROM

HERE

z

'200V OHMS

r--(1)1TIBBP

IS HY. CHOKES

,- PT Iloti A.C.

5,.,.*r Schematic circuit of the amplifier. Note the use of a 57 direct coupled

into a 46, class A amplifier.

TODAY, more than ever before, public address work offers money- making opportunities for wide -awake Service Men who have the gumption to go out after business. Amplifiers and accessories are available

in great variety to suit numerous purposes, and their prices have reached levels that were considered impossible only a few years ago. You can quote reasonable figures for even large installations and still make a profit.

The public -address field is the first branch of the radio industry to benefit directly from the recent avalanche of new tubes. While receiver manufacturers actually threw up their hands in despair and pleaded for mercy, P.A.specialists, not hampered by slow acting research departments, swung right into production with amplifiers that took full advantage of the new types. A good example of this quick work is the 28 -watt class "B" unit described later in this article.

You must not expect business to fall into your lap without effort on your part. Acquaint yourself with the various public places of your city and consider them all as prospects. Even in very small towns there are many promising possibilities. As prospects for permanent indoor installations of small or large size, jot down the names and addresses of all the local establishments of the following classifications: churches, dance halls, skating rinks, lunch wagons, restaurants, schools, factories, lodge halls and auditoriums.

How fo Get Business

Go after the churches first. Because of their very size and architecture, their acoustics are usually pretty bad, and many a good preacher finds himself handicapped by

*Sound Engineer, Wholesale Radio Service Co., Inc.


ALL Service Men appreciate the value and effectiveness of public address amplifiers for

many purposes, but few know just how to go about selling them to live prospects in their own towns. In this article, the first of a series, Mr. Short gives some practical, common sense suggestions, based on his own extensive experience in the field. He has designed, sold and serviced many different types of amplifiers and offers his services to readers of RADIO -CRAFT.

MAKING MONEY

WITH

P.A. AMPLIFIERS HUBERT L. SHORT*

his inability to make his natural voice heard in the back rows and in the balcony. The use of a P.A. amplifier and a few judiciously placed loudspeakers has increased attend- ance at more than one house of worship.

Of course you want to make sure that any particular church would benefit by the addition of a P.A. unit. Simply attend yourself and make personal observations on the spot. This is the only way to prepare yourself for any sales campaign. In business, as in war, preliminary preparation is half the battle.

Dance halls and skating rinks, which are the main places of amusement in many towns, are "naturals" for the Serv- ice Man. Look up the places that now use only three- or four -piece bands or perhaps a radio receiver that is over- loaded beyond the point of respectable quality. Talk to the owners and show how they can make their halls more attractive by playing selected, high -grade phonograph records, made by the most expensive bands in the country, instead of annoying the customers with a sour saxophone or an untuned piano. Tell them how they can stage "radio talent" nights, by getting the local Rudy Vallees and Kate Smiths up in front of a microphone in the middle of the floor. All they can do is say no. Don't be discouraged by the first refusal. Keep after them until they finally threaten you with bodily harm. Very frequently persistence will win out.

Lunch wagons and restaurants in many cases prefer coin operated automatic phonographs to manually controlled amplifiers, but don't pass up any bets. Some of these so- called "lunch wagons" on the more heavily travelled automobile highways are very large and are beautifully and often expensively fitted out, and their patrons rather expect some sort of music without having to push nickels into slots.

Most communities are very proud of their schools and will spend considerable money on them in preference to other municipal undertakings. Therefore by all means approach the school board and present the idea of a public address amplifier for general use throughout the school building or buildings. In many schools a microphone is permanently located on the principal's desk, so that he can make announcements to all classes simultaneously through


353



RADIO -CRAFT KINKS Practical Hints From Experimenters' Private Laboratories

Prize Award A POCKET RADIO SET

Lawrence B. Johnson

HATS off to the radio set that uses no tuning coil or tuning condenser,

but which gets a station just the same! This arrangement, illustrated in Fig.

A, has no selective characteristics but makes it possible for you to enjoy that particular high powered station above all others. This may be seen by reference to the schematic circuit, Fig. 1A. Condenser C in series with the antenna affords a slight degree of selection; one side of the connection to a little wire clip which goes around the threaded portion of the electric light bulb, and the other side of the receiver circuit is grounded, as shown at B in Fig. 1. A crystal detector mounting is arranged inside the headphone as shown at C. The writer will be glad to explain any details which are not clear.

Fig. A Ah! The " tunerless" receiver at last.

LIGHT ANTENNA

-A-

-

ANTENNA

, -

0

LINE

CLIP

-

y

HEAD- PHONE COILS

CRYSTAL

C PHONE CORD t

UNIT

CL

LAMP Y f

OA e

4 SLIP CLIP ONTO METAL ON

GLOBE

®r' ;

iJ CONDENSER l ' - WATER

D -- - PIPE GND CLIP 500 HMG /

LAY DETECTOR FIBER ON TOP OF CONTACTS OEODTR0.

HOLLDER CRYSTAL

(QOA; TJ ` l 1

B b

SPRING WNI3KER

A B CRYSTAL 1 :. 4 HOLDER

BOLT FIBER AND NUT BASE

Fig. I

Detailed schematics of the "funerless" receiver.

354

$5 For a Practical Radio Kink

As an incentive toward obtaining radio hints and experimental short -cuts, "Radio- Craft" will pay $5.00 for the best one submitted each month. Checks will be mailed upon publication of the article.

The judges are the editors of "Radio- Craft" and their decisions are final. No unused manu- scripts are returned.

Follow these simple rules: Write, or prefer. ably type, on one side of the sheet, giving a

clear description of the best radio "kink" you know of. Simple sketches in free -hand are satisfactory, as long as they explain the idea. You can send in as many kinks as you wish. Every- one is eligible for the prize except employees of "Radio- Craft" and their families.

This contest closes on the 15th of every month, by which time all the Kinks must be received for the next month.

Send all contributions to Editor, Kinks De- partment, c -o "Radio- Craft," 98 Park Place, New York City.

BATTERY LUG PLIERS Welter Luhrs

RADIO men too often resort to the use of a hammer to remove cable lugs

which have become corroded to storage battery terminals. However, the special pliers illustrated in Fig. 2 perfectly solve the problem. On an emery wheel, grind to a tapering point the outside faces of a pair of "chain" pliers; this tool may be obtained from an electrical supply house.

A SENSITIVE CRYSTAL SET

J. M. Nighswander

T0 date, the writer has picked up the signals of KFI, 750 miles distant,

with sufficient strength to hear them in a room 12 x 16 feet, using the receiver which is connected as shown in Fig. 3. On some nights, 12 to 15 Pacific coast stations can be tuned in at my location in Eugene, Oregon. The parts used by the writer are as follows:

One lump of galena for the crystal detector; one 500 mmf. tuning condenser, Cl; one .001 -mf. bypass condenser, C2; one coil form 5 x 3 in. in dia., wound with No. 18 D.C.C. wire and tapped as shown, L1; under this coil wind the secondary on a form 2T /e in. in dia. The latter winding consists of 11 T. No. 18 enam. wire, spaced one turn; slide this coil, L2, inside the primary, Ll; two tap switches complete the assembly.

The range of this receiver is roughly from 126 to 800 meters.

The writer can readily prove the reception claims made for this efficient set.


BRASS BRAC¢ET LEADS TD

AMPLIFIER

AUDIO TRANS.

LEADS TO

AMPLI GIER+

B- TI

OUTPUT J

c)..13+-

Fig. 4 Here's a real oscillator that should find a berth in

any experimenter's lab.

Fig. 2

Truly, an ingenious scheme. Fig. 3

Well, readers, what do you think of it?




THE RADIO CRAFTSMAN'S PAGE

THANK YOU, KIND SIR

Editor, RADIO- CRAFT:

Just opened the November issue of RADIO -CRAFT, and read with a great deal of interest and a lot of hand - clapping your editorial. Go to it! The more truth there is put forward so that people in the industry can read it, the better off we'll all be.

It's too bad the great American public has never learned the lesson that you usually get what you pay for in this world and not a whole lot more, and I agree with you that the Radio business has actually suffered the loss of business on account of the fact that they have not seemed to sense the fact that people are perfectly willing to pay money for something if they get value received.

Again I congratulate you on your editorial!

With best regards, I remain SAMSON ELECTRIC COMPANY, R. W. COTTON, SALES MANAGER.

A LA PENTODE PORTABLE Editor, RADIO- CRAFT:

I am writing you of my experiences with the "A.C: D.C. Pentode Portable Receiver" described in the September, 1931 issue of RADIo -CRAFT magazine. I am very well satisfied with the results, although I was unable to obtain any reception using the tuning system described in your magazine, probably because of my location.

With a few alterations in the tuning system, I was able to receive stations that other 6, 11, and 12 tube radios could just barely get. I live near the Bingham substation where six, 44,000 - volt lines meet at a common bus. My antenna is within 100 feet of this bus! Yet, with my hookup, I am able to bring in Denver, Texas, Los Angeles, and, of course, all local stations.

The sketch of my receiver is shown in Fig. 1. I hope it may be of some use to you or to some of your readers. Referring to the diagram, the parts are described as follows: Ll and L2 are wound on the same form which is 3- inches in diameter; Li is wound with No. 28 D.C.C. wire and has 30 turns; L2 is wound with the same size wire and has 40 turns. Coil L3 is on a 1z4- inch form and has 10 turns of No. 26 D.C.C. wire. The spacing between the coils is not critical at all. Condenser C has a capacity of .0001 -mf.; and CI and C2 each a capacity of .00035 -mf.

IMPORTANT NOTICE In the interest of those readers who do not

like to mutilate this magazine, we have asked our advertisers not to place coupons in their advertisements.

Instead of the usual coupons, you will find a number of convenient post cards inserted between the last page and the back cover of this magazine.

This new service will save you time and work. No need to cut coupons, nor is it necessary to hunt for and address envelopes. More- over the space for your name on a coupon is

usually so small that the advertiser is often not able to make out your writing and then you wonder why you do not get the literature sent for.

Then, last but not least -the postage for a

postal card is only 2c whereas a letter now costs 3c.

Road the advertisements and then turn to the page containing the special postal cards. Detach, fill out and mail the card of the advertiser whose literature or offers you went to have sent to you.

Mail your card todayl Show the advertisers that you appreciate their cooperation and thoughtfulness.

Fig. I

This gentlemen claims wonders for this circuit - we wonder if you wonder.

Hoping that this little sketch will be of some value, I close.

MAX SPENDLOVE, P. O. Box No. 4,

Bingham. Canyon, Utah. (Thank you Mr. Spendlove. And now

readers, suppose you try it and let's know the verdict. -Editor.)

MORE RADIO -CRAFT CIRCUITS Editor, RADIO- CRAFT:

I was very much interested in that excellent a r ti c le "Non- Regenerative Amplification," by Mr. Cusick which appeared in the August issue of RADio- CRAFT. Will you please try and give us another article on the same subject which will emphasize its application to short waves; the I.F. section of supers;


The Bulletin Board for Our Experimental Readers

and the changes necessary to accommodate the various types of tubes?

Here's hoping you give us another of your RADIO -CRAFT circuits showing us how to adapt these principles to our own use.

FRANCIS C. WOLVEN, Route No. 2, Box 103,

Saugerties, N. Y. (We'll try our best, kind sir, but

please remember that we can only run data that we believe will be of general interest. Editor.)

AHI A COMPLAINT Editor, RADIO- CRAFT:

I have taken quite a bit of interest in your publication for several past years and today have been reading the Sep- tember issue. In going over the article by S. H. Burns entitled "How to Build a High Gain T.R.F. Receiver," I find no reference to speakers at all, other than a connection shown on the schematic.

This is true of most designs for both long- and short -wave receivers. Now I would like to know why these articles deal with receivers but pay absolutely no attention to the speakers (or phones) used with them. Is a speaker of no consequence? To me a completed receiver is only as good as its speaker or phones. Why don't the radio industry take a tip from the automobile industry, and learn from its mistakes? Old cars never had a windshield, but today they are being made with spare tires, and even come equipped with complete radio installations!

Other than the above, you have a good magazine.

F. R. GALE, Balsam, N. C.

(In the first place, most articles treat the procedure to follow in building a receiver -not a speaker. In the second place, a good many of the constructors already have speakers that are perfectly O.K. for the purpose, and the specification of some other make might convince someone of the necessity for purchasing an additional speaker. This is what we wish to avoid -too much expense. In the third place, a completed receiver is not always as good as its speaker. Old timers will recall the days of 1922 when a poor receiver with a worse speaker sounded better than the same set with a better speaker -because the better speaker reproduced the distortions of the poor set, while the bad speaker did not! -Editor.)

355



Fig. A External view of the receiver. All parts are labeled for convenience.

Fig. B

Under chassis view. The simplicity is evident.

THE general trend of short -wave receivers during the past few years indicates that the barriers against the use of

A.C. power supply which prevailed, have slowly, but surely been broken down. Due to the remarkable improvements in present -day tubes and developments in circuit design, the completely A.C. powered, short -wave set may be built with less trouble and greater power output than a battery set. Short -wave manufacturers have been marketing A.C. receivers for the past few years, but the amateur and shortwave fans have been skeptical of their actual worth. The successful performance of A.C. broadcast receivers has altered the outlook toward the use of A.C. for the shortwave receiver.

The numerous objections to A.C. operation may be summed up in one fact -too high a hum level for both phone and speaker reception. Curious as it may seem, A.C. amplifiers are accepted in conjunction with a battery powered set; but full A.C. operation seems to be either a catch -as- can affair, or just a lucky break.

Fortunately, certain mechanical improvements in battery sets are largely responsible for practical A.C. operation. They are: (1) Complete shielding of all coils and tubes in R.F. and detector stages; (2) Adequate bypassing of all power -supply leads; (3) elimination of plug -in coils by the use of fixed coil forms which are gang controlled.

Because of absolute necessity, this set includes these features. Besides these, the greatest gain is secured by taking full advantage of the high voltage necessary for the operation of power amplifying tubes. The receiver embodies an R.F. stage; a regenerative detector, audio and a power audio output stage. The wavelength covered is from 10 to 200 meters by a gang -controlled, four position knob.

The operating features of this receiver are: (1) Low hum level permitting phone and speaker use; (2) single wavelength- change control; (3) single control tuning dial; (4) loudspeaker operation.

The schematic diagram of the set is shown in Fig. 1. The

356

CONSTRUCTING THE

TRIPLE -TWIN S. W. RECEIVER

H. HARRISON

description of the set will be given by treating each stage as a separate unit.

The R.F. Stage The tube in this stage is the type 58. The proper opera-

tion of an R.F. amplifier preceding a detector should be: (1) No effect on the regeneration action of the detector; (2) no effect on the tuning in the detector stage; (3) this stage must amplify -not "block" the signal.

In effect, the R.F. amplifier must be absolutely isolated from the detector in -so -far as actual detection is concerned. Primarily, all the desirable effects are almost obtained by separate coil and tube shielding. It is far more important to have effective shielding than to worry about the extremely small interstage leads. In this particular receiver, no added gain was obtained by shielding the small inter - stage leads. Another absolute requisite to the proper amplification of the R.F. tube is the bypassing of all voltage - supply leads. The inclusion of these condensers prevent the flow of R.F. into the voltage supply circuit and also reduce the possibility of hum pickup.

The selection of an R.F. choke proved to be more important than at first thought. The R.F. choke, CHi, has a large effect on the input to the detector stage and therefore must block all R.F. out of the power supply. The combination choke and condenser, CHi and C5, may be considered as a high -pass filter. The R.F. will flow through the condenser since this is the path of lower reactance. Within limits, the greater the capacity of C5, the greater will be the input to the detector. The ratio between the reactances of CHi and C5 should be as great as possible, since the larger this ratio, within limits, the greater will be the input to the detector. It can be seen, therefore, that only a short -wave R.F. choke which has a large reactance and small capacity in all the working frequencies can be used.

The coupling condenser C5 is larger than ordinarily recommended, but it is permissible here because of the excellent R.F. choke used.

Tuning is accomplished by the large tuning dial shown in Fig. A. The ganging of both R.F. and detector stages was made possible only by careful construction. The volume is controlled by the potentiometer R12.

The Detector Stage A type 56 tube is employed as the detector. Regeneration

is smoothly controlled by R3. The usual detuning disadvantage of condenser regeneration control is not noticed in this system. The regeneration circuit control consists of a fixed condenser, C4, and the variable resistor R3. Addi- tional amplification is gained by the use of the A.F. transformer, Tl. Tetrode detection was tried, but due to the fact that plate- and grid- circuit filters were found necessary in the R.F., the detector and 1st A.F. stage in order to reduce R.F. interstage coupling and to reduce the hum pickup, it was abandoned in favor of the triode.

It must be borne in mind that the coil forms were wound for triodes; a screen -grid detector would necessitate rewind- ing and adding to the tickler turns. The use of a trans-




I

A short -wave receiver using the latest tubes avail-

able, and one of the most sensitive for short -wave

work that has come to our attention for a long time.

It is all A.C. operated and has enormous volume.

WHY THIS SET IS DIFFERENT It is all A.C. operated, thus eliminating troublesome batteries; uses the variable -mu type of tube; reducing interference and noise pickup to a minimum; employs regeneration, which further increases the sensitivity; the triple-twin tube in the power stage results in considerable power output which is perfectly controlled, manually; a tone control - which changes the pitch of the voice or music heard. This

device also helps to reduce background noise.

former has the added advantage of reducing the hum. As before, the R.F. choke, CH2, was found to be important. The same type of choke as that used in the R.F. stage was finally selected. Both the R.F. and detector coil forms are ganged and controlled by a single knob.

There are four positions covering the following ranges: 200 -80 meters; 80 -40 meters; 40 -20 meters; 20 -10 meters. A small trimmer condenser, C6, provides correct line -up of the dual condenser. This is initially adjusted at about 150 meters. It has been found that no additional adjustments are needed at any other frequency. If the tube does not regenerate, reverse the tickler winding. The new 4 -inch National type N dial permits fine tuning.

RF. COIL

SHAFT I/2 INCH

COPPER BELT

DET. COIL

FASTENING BOLT

HOLDING BOLT

DRUM

DIRECTION OF ROTATION

COIL FORM SHAFT

l

DRUM FRONT KNOB of PANEL

al i - InRodomml

i4 KNOB

tik

DET. '1,1I

SHAFT COIL -tyll COUPLING SHIELD ll

EXTENSION SHAFT

-B-

Detail Fiq. 2

illustrating the method of coupling the "belt" to the condenser shafts.

The A.F. Amplifiers

The '27 is the first A.F. tube; the triple -twin type 295 being the power- output amplifier because of its good frequency response. The operating performance of this tube is such that with a lower input, it will deliver a larger output than the '47. The principle of operation of this tube makes it imperative that the cathode and grid -bias circuits be carefully followed. The choke CH5 should have a minimum value of 20 henries.

To reduce the possibility of distortion and hum pickup, the grid bias resistors must be adequately bypassed. This is especially true for the 295 tube, where a 25 mf. condenser is necessary. The values given for the other bias resistors should be adopted. Headphone reception can be obtained by plugging into the phone jack, mounted on the back of the chassis. The output transformer, T3, may be connected to either a magnetic or dynamic speaker. If a magnetic speaker is used, substitute a 1,500 resistor for the dynamic field, CH4, capable of carrying 125 m.a. Another 30 -henry choke may be substituted and a smaller resistor will be necessary. Where a dynamic speaker is on hand,

be certain that the field resistance does not exceed 1,500 ohms. For coupling to either type speaker, the effective primary impedance of T3 must be 4,000 ohms.

The Power Supply

The rectifier tube may be either an '80 or the new 83 mercury -vapor rectifier. If the 83 is used, it will be necessary to connect a small 3 milli- henry, 250 ma. choke at point "X," in Fig. 1. Leaving the choke out of the circuit may introduce a hum.

The care expended in the receiver proper may be completely nullified by a poor filter circuit. Ripple -free D.C. is absolutely essential for operation of the receiver. This can only be obtained

by suitable design of the power supply. An A.C. hum may be introduced by the power supply by

mechanical or electrical faults. Included under the list of mechanical means of producing hum is the magnetic inter- action of the A.C. power transformer to the filters or R.F. coils by close physical location, or by vibration of the cores. To overcome these possible and undesirable effects, it is necessary that the components be separated by a suitable distance or that they be shielded from one another. These precautions have been carefully followed. The greatest chance of hum input comes from the filter itself. This filter is a one section pi type. It cuts off at about 40 cycles. This is below the line frequency, and therefore eliminates any hum pickup through the line circuit. Only one filter choke is needed. It has an inductance of 30 henries at a safe current -carrying capacity of 125 ma. The filter condensers, C10, are "dry" electrolytics, having a very low leakage current. The filter parts are mounted beneath the chassis (Fig. B), thus being entirely shielded from the power transformer, although the choke and condensers are not indi- vidually shielded.


f LI r`r,

Ì° gl

ci

I

Ì Ì

58 C5 I L2 1!

R2

REGENERATION CONTROL I CH. Z.1

C4 '1)88/17. + /

X2 R3

C2

I L. 1

C3.4 R12

C6 X x

GND

VOLUME 7

CONTROL

'27

X3

X

xTa

C2

C2 R4 PHONES

/

R R

L CHASSIS Rll RIo R'9 RB

T2

TRI N 295 { T3

R7' . R6

C9' CH 4 52

x

,eo

v5

SW

PT

RI3

Complete schematic circuit of the receiver


Fiq. I

Refer to the List of Parts for all circuit constants.

357



RADIO -CRAFT'S INFORMATION BUREAU SPECIAL NOTICE TO CORRESPONDENTS: Ask as many questions as you like, but please observe these rules:

Furnish sufficient information, and draw a careful diagram when needed, to explain your meaning; use only one side of the paper. List each question.

Those questions which are found to repr t the greatest general interest will be published here, to the extent that space permits. At least five weeks must elapse between the receipt of a question

and the appearance of its answer here. Replies, magazines, etc., cannot be sent C. O. D. Inquiries can be answered by mail only when acompanied by

25 cents (stamps) for each separate question. Other inquiries should be marked "For Publication," to avoid

misunderstanding.

BLUE GLOW VS. PURPLE FLUORE- SCENCE- OSCILLATOR COUPLING

(180) Mr. John Bold, Kansas City, Mo. (Q.1.) 1 have a type '47 pentode which

shows a purple glow on the bulb. The tube seems to operate satisfactorily, but I understand that this is a sign of possible break- down in a short time due to ionization. Is this the case?

(A.1.) The following data regarding this phenomena has been released by Sylvania. The effect on the glass bulb of the tube, a purple fluorescence, is not due to the ionization of gars within the tube. but is caused by the impact against the glass of certain of the X-rays generated within the tube itself through chemical reaction between the "getter" and parts of the tube. Gas. on the other hand. manifests its ionized condition as a blue plow around the plate.

Usually, the blue glow of ionized gas at the plate does not change appreciably with changes in the signal volume as does the fluorescence on the glass envelope due to X -rays. As far as we (Sylvania) have been able to determine, the glow which appears on the glass walls of the tube does not in any way affect the tube, or reception conditions.

(Q.2.) Isn't there an error in the diagram of the 3 -tube circuit in the article, "The '8 -Tube' Autodyne Superheterodyne," in the August. 1932. issue of RADIO -CRAFT, pg. 86? There does not appear to be any coupling between coils L2 and L9 in order to obtain operation of the oscillator portion of the circuit. Isn't there a connection lacking between the B end of L2, and the ground side of coil L3?

(A.2.) The diagram as shown is correct. However, the illustration would have been a little more clear had inductance L8 been shown in inductive relation to L2. It is actually wound on the same tube in order to provide the necessary coupling. As a matter of fact. L3, L2 (both coils) and IFTI all combine to produce what is termed a "composite oscillator- intermediate."

ER -LA TUBE CHARACTERISTICS (181) Mr. A. N. Claridge, Baton Rouge, La. (Q.1.) What are the static and dynamic, and

also the distortion characteristics of the Ever - eady type ER -LA tube?

(A.1.) These figures are given in the article, "More New Tubes," by Louis Martin, in the May, 1932 issue of RADIO- CRAFT, pg. 683. The static figures are represented in more detail in Figs. Q.181A and B. and the dynamic values in Fig. Q.181C; additional figures taken from experimental data are shown in Fig. Q.181D. The distortion characteristics of this type tube are given in Fig. Q.1S1E.

2.0, 20

1.5 IS

3Loiólo

wSu15 WÓ

Oo. 0 O IO 20 30

INPUT VOLTAGE ACROSS THE M° GRIDS- VOLTS RM5

- ER - LA ---ER-'18 -- ER -'d7

111111111Mmil

v/0e] EN HRTIOOHIC E

PKZEIROM

C bp p PILOT "WASP" SHORT -WAVE

RECEIVER (1821 Mr. Eric Svengeld, Lewistown. Ill. (Q.1.) What is the schematic circuit em-

ployed in the Pilot "Wasp" short-wave receiver?

(A.1.) The diagram of connections followed in the "Wasp" receiver are shown in Fig. Q182A. However, it may be to some advantage if we call attention to other variations of the "Wasp" receiver, diagrams of which have already appeared in RADIO -CRAFT, to wit:

"Super- Wasp," July 1929. pg. 22; "A. C. Super -Wasp," Jan. 1930, pg. 310; "Universal Super-Wasp," April, 1931, pg. 604. The original "Wasp" circuit shown in Fig.

Q.182A. bears little resemblance to its ramifica- tions listed above. The A.F. transformers A.F.T.1 and A.F.T.2 may be any desired make; the ratio may be, for instance, about 3.5 to 1. Regeneration is controlled by the two 100 -mmf. variable condensers connected in parallel. Note the extremely small capacity of antenna con-

denser C. The plug -in coils may be those used in the "Super- Wasp" set. It should be noted that many experimenters prefer to use higher values of grid leak resistance, often as high as 8 or 10 megs; also, the majority seem to prefer to use a grid condenser of 150 mmf. The best value to use for the fringe -howl suppressor, in shunt with the secondary of A.F.T.1, is best determined by experiment.

(Q.2.) In Part I of the article, "Simple Radio Mathematics for the Service Man." by Boris S. Naimark, which appeared in the September, 1930. issue of RADIO -CRAFT was shown a formula for power factor which seems to be in error. Please advise whether this is the case.

(A.2) A correction of this formula appears in Fig. Q. 182B. The same correction also applies to the reproduction of this series in the book "Radio Questions and Answers," by R. D. Washburne, pg. 59.

Cosine $ -1, Sine (6 -' ' and Tangent 4- Fig. Q.182B. A formula correction.

FI

C ó L3 2MEG

SHOOT ANT P

G

LI -

ti LONG F2 ANT

N L2

TT ONO

.0002- HF

.00014-Mr v

'014 !

RFC A.F.TI r000

c D

ÌR+'Ì OOOI NF (EACH)

0+

.01A

G

F- 0.1- MF

AFT2 '01A

V2

10 0111.15

AL, 8-I -15+.01T C -.000015-MF

PNONE5

Fig. 9.182A. Schematic circuit of the Pilot "Wasp" short -wave receiver. This is the diagram of a set which in its day, now long past, had no peer. Although type '01A tubes are indicated in the figure,

other types of triodes may be tried experimentally.

., 1S 2.5

Ell- 20 2.0

=u m

15 r1.5 ° ìs

XzI0wsN1D

F 3 S .5

0 0

o

1:-:¡U$ .1\ . MO, EC EMIKIENS 111112

OUTPUT yPOWER

r PLATE r,cURRENT

1j RR j HAaMONIC

DISTORTION

10000 20.000 10000 LOAD IMPEDANCE (OHMS)

PLATE CURRENT

SCREEN-GRID CURRENT --

-30 -20 -10 CONTROFGRIO VOLTS

50 o

40 w

s°lu ° 30 = zof

w W 10 á

0

a

0

'g. Q.181 A. Characteristic data on the type ER- F q. Q.181 B,

LA tube described in RADIO. CRAFT. Comparative

358

I.tS

1.0

r2 .75

3 N .S

a .25

5A HARMONIC DISTORT ON

5.000 10,000 15.000 LOAD IMPEDANCE (OHMS)

5 CONTROL GRID VOLTAGE (ECI) -O

20

25 50 75 100 125 150 175 200 PLATE VOLTS

above, and, Fig. 9.181C, below. F g. Q.181D, above, and, Fig. Q.181E, below. data on Eveready vacuum tubes. Distortion characteristics of the ER -LA tube.




Here comes the

Official Radio Service

Manual

'19194913Rdb R«n.n.

.n R. Sn.:e ow.

$5.óo

OVER 2,000 ILLUSTRATIONS

OVER 700 PAGES

9 x 12 INCHES

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FLEXIBLE

LEATH ERETTE

COVER

1933 Official Radio Service Manual The importance of the last two OFFICIAL RADIO SFRVICI- \IANCALS to those engaged in the Radio Industry has been shown by the fact that over 52,000 copies of both editions have been purchased and are in use by manufacturers, jobbers, dealers, Service Men and experimenters. Incessant demands have en- couraged us to publish a new and bigger Service Manual for 1933.

The new manual will not contain so many full -page illustrations as in the past for the reason that not as many new sets are being put out at present, but will have in its contents important information that has not yet appeared in print. This new "dope" is invaluable to radio men. Stress has been emphasized on giving only practical material, not complicated theory. It is bound to save time and money for everyone. The simplicity in the makeup of the 1933 Manual makes information easy to find, accurately and quickly. As in the past the size will be 9 x 12 inches, in loose - leaf form, with flexible leatherette covers. Many additional features will be included in the new manual. The FREE QUESTION AND ANSWER SERVICE which was extremely popular in the previous edition will also be maintained. We assure you that the 1933 OF- FICIAL RADIO SERVICE MANUAL will be a revelation in radio literature. Advance orders are now being accepted at the price of S5.00. Take advantage of this low price -send your order today. Be among the early ones to get a copy from the first printing. Checks or money orders accepted -register letter if it contains cash or unused U. S. Postage Stamps.

The following are partial contents of the 1933 Manual: Complete operating notes, and hints from actual experience with radio receivers

in the field, collected by practical Service Men all over the country. Complete actual, pictorial views of hundreds of commercial receivers with addi-

tional schematic diagrams. Location of parts on the chassis are shown, and where important adjustments must be made. This section alone is worth the price of the book.

Values of all intermediate frequencies used in superheterodynes, and a complete section of valuable service data on superheterodynes.

Values of resistors and condensers, to aid in replacement work. Latest information on combination long- and short -wave receivers, short -wave

adapters and converters. How to tune and service short -wave receivers for best results. How to use the most modern servicing instruments. Complete section showing how the Service Man can build himself service instru-

ments, oscillators, etc., at very low cost. Complete section on the construction of all test equipment, including high- and

low -frequency oscillators, tube checkers, ohmmeters, etc.

Tube -chart information on all new and old tubes, in handy form for quick reference; indicating socket connections and operating values, thereby preventing confusion.

An entire section on money -making suggestions for Service Men, written by the Service Men themselves who have made a success of the business; giving you short cuts and commercial information on how to get the most out of the servicing game.

Servicing information on interference elimination, with practical data and many examples of interference prevention.

Automobile radio installation and servicing -hints on automobile radio in general. Complete data on servicing all known, commercial, automobile receivers with short cuts to get quickly at the seat of the trouble.

Service kinks, servicing short cuts, and miscellaneous servicing information. A complete section of various radio tables of every imaginable kind, in constant

use by up -to -date Service Men. A large section giving complete technical data on meters of every kind pertain-

ing to servicing in general. Complete index and cross -index to make it easy for you to find

almost anything pertaining to service instantly. GERNSBACK PUBLICATIONS. Inc. 96.98 Park Place, New York, N. Y.

I am en, losing herewith toy rein loan. of $5.00 for which you are lo send u MT of the 1933 OFFICIAL )tAnñ1 SRltt'IC'F. MANUAL at the price of

at-h. Cher ks or am o

1 ney orders Register letter 1f it contains rash or unused U. S. postage stamps.

Name

Address

City Stale

FREE

QUESTION AND

ANSWER SERVICE

In every copy of the 1933 Manual, 24 uupons will be

luund, which will entitle you to 24 thorough and complete answers by mail on servicing :md operating on any of the sets or circuits mentioned

n the manual, as Well as any others tot mentioned, for .which you might la rve need. This service alone is worth 46.00. But it is absolutely free to manual owners.

THE OFFICIAL RADIO SERVICE MANUAL FOR 1933 COMES TO YOU COMPLETE

THIS YEAR -NO SUPPLEMENTS




Make BIGGER PROFITS this year by replacing with ARCO New Life Radio Tubes

Gave to your rustmners the advantage of buying first-quality licensed It C.A. tubes at prices that are exceptionally low. We retry the largest variety of tubes in the world, many for special purposes, and every tube is replaceable within three months, providing the filament is not burnt out. We either hare the tube you require or we will make it for you. COMPLETE STOCK READY FOR IMMEDIATE SHIPMENT

Order from this pace -Remit 20% with order. balance C.O.D. All Prices are F.O.B. FACTORY, Newark. Shipments go forward express or parcel post. No order for lesa than $3.00 accepted. TYPE ANY QUANTITY UX- 201A- Amplifier or detector....._...._...._...._.. __.._ $0.30 UX -226 -AC amplifier .30 UY -227 -AC amplifier or detector .30 UX171 -Same characteristics as 171A on tungsten filament.

.30 UXI71A -Power output amp. for AC or DC operation, t4 amp .30 UX -240 -Designed for impedance and resistance coupling..._ .40 UXI20 -Power amp. used In last stage of audio freq. ..... __ .40 UX(99 -Detector and amp. tube, long prongs .40 UV -199 Standard base, has a 201A base. saute characteristics

as 199 .40 UV -199 Same characteristics as UX -199 only short prongs .40 UX -I12A -Parer step. tube for low cur. conswnp.. 'H map .40 UX112 -lower Amp. % UX- 200A- Detector tube recommended for weak signals _._. 0 UY224 -.LC screen grid amplifier _...__ .... ....... .40 UX245 -Power amplifier .40 UX- 201B -y. Amp. Amplifier and Detector .60 UY- 246 -Power Amplifier .60 ÚY247 -Power Pentode .60 WD -ii -Detector Amp .60 WD -12 -Detector Amp UX -230 -Dry cell atop. and detector. 2 volts .60 UX231 -Dry cell amp. -last audio stage. 2 volts. .60 UX -232 -Dry cell screen grid amp., 2 volts ...__.__ .60 ÚY233 -Power Amplifier Pentode. 2 volts .85 UX -234 Screen Grid Pentode 1t.F. Amplifier .85 UY -235 -Super control screen grid amp __ _._ 60 UY -236 screen Grid Radio Freq. Amp .85 UY -237 -Detector Amplifier .85 UY -238 -Power Amplifier Pentode .85 UY239 -DC R.F. Pentode Amplifier _. .85 UY -551 -Variable Mu .60

41 -Power Pentode .60 55 -Duo Diode Detector .... .60 56 -.t.1 -'. and R.F. Amplifier and Oscillator.... .

57 -al prong Screen Grid R.F. Amplifier and Detector 58 -6 prong Variable Mu R.F. Amplifier and Super Detector 59 -Parer tmplider

-Duplex Diode Triode 6 prongs ever Amplifier 6 prongs -For power high voltage

-Screen grid radio frequency map

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wish

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60 89 A 1 fl p - - .60

UX222 d 1.10 1.10

B Ballast

-lower even used in last stage of wing out

1.10 Spriest tube -r Iva tubes In net front blowing out I.10 Special super -sensitive Audio Freq. 201A .60 Special super-sensitive Media Freq. 201Á .60 Special 171 AC High

amp. high

coated filament-good for elrrl sir s.t. .60 e oe S-ii (201A Hlgh 2igh 171a double . .60 Switch tune. 22. 112 or Ilo douelt Ilia .60 tube tam 22e 1r1de to convert bat. web to

quick each_. .60 UY- 224A -AC amplifier or mplifie same as 227 (but gquic nheeler, .60 ÚV22 /A -AC screen grid amplifier. same as 224 (but quirk heater.. _. .60

RECTIFIER AND CHARGER BULBS 125 5111. rectifying tube (It. IL) (Raytheon Type) 6/10 amp. trickle charger bulb (Tunear Type) 2 amp. old and new type charger bulbs (list $4.005 ( Tunear Type) 5 and 6 amp. charger bulbs (list 43.00) ( Tunear Type) 15 amp charger bulbs (Tunes, Type) UX -866 -llot Cathode Mercury Velar Half-Wave Rectifier UL.iss I UX280M -Ilot Cathode Mercury Full -Wave Rectifier same as t-\ -Ja3 UX- 281M-Ilnt Cathode Mercury Vapor half -Wave Rectifier UX -1171 -lint Cathode Mercury Vapor Rectifier

UX -280 -Full -Wave Rectifier for High Emission..._ UX -281 -Half-Wave Itertiller U X-282 -Full -Wave Mercury Vapor Rectifier UX -283 -Rectifier UX -216B- Half -Ware Rectifier UX -213B -Full -Wave Rectifier

PHOTO CELLS Photoelectric cell. "Potassium" Type 0 _....._ ..... ...... 2.10 Photoelectric cell, "Caesium" Type A, 434" overall length 7.90 Photoelectric cell. "Caesium" Type R, 3 1/18" overall length 5.90

TELEVISION TUBES Telion Refeetron Neon Television Tube. 1" Cathode Square Type C . 3.85 Telion Neon Television Tube. l% Cathode Square Type V .. . 3.85 Telion Neon Television tube. l' Cathode Square Type X 2.10

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UX- 182 --Sparton UX -183- Sparton Type UY- 484 -Sparton Type U X-585-Sparton Type UY -686- Sparton Type UX401- Kellogg Type UX- 403 -Kellogg Tape___

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Write for our new prier list and ! ethnical data. Amplifiers front $9.85 up.

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On page 359 of this issue will be found an important announcement of the 1933 OFFICIAL RADIO SERVICE MANUAL. It is worth your while to spend a few minutes reading this adver- tiament which telle in detail all about the contents of the New Manual.

360

QUASI -OPTICAL EXPERIMENTS

John B. Brennan THIS is the third of a series of short. simple articles, regularly appearing here. The purpose of them is to describe an easy experiment monthly with apparatus

which the ordinary experimenter, engaged in the building and rebuilding of broadcast receivers and associated equipment, has undoubtedly accumulated over a period of years.

Radio, in its popularly accepted sense, is generally regarded as that form of entertainment which is transmitted from the hundreds of transmitting stations scattered all over the world. More specifically, in the United States of America, it is that band of frequencies lying between 546 and 1500 kilo- cycles (200 to 660 meters)

But actually, this kind of radio, as we have come to know it, forms only a small part of the entire communication service. At the upper end of the frequency spectrum (down in wavelength) there are the shortwave communication services, while at the other end (long waves) are the older, long - wave communication services.

Years ago, more attention, from a communication standpoint was paid to the so- called long -wave transmitters, but now, due to countless experiments, not a few of which are directly traceable to the amateur radio enthusiast, much has been learned of the marvelous carrying powers of the short waves (high frequencies).

Much activity abounds in the amateur, five - meter band. Experiments are daily engaging the attention of engineers in the % -meter band, and so low in wavelength have these experiments gone that now we talk not in terms of wavelength in meters, but in centi- meters.

Then, down below that band of wavelengths which have actually been used for communication purposes. there exists that band of frequencies so short in wavelength (high in frequency) that they border on the frequency of light waves. It is because of the border- land character of these waves that they have. for the time being, been termed "quasi -optical" waves, and it will be with experiments in this field that we will be ultimately concerned. Strictly speaking. the experiments described in this department, so far, have not been of the quasi- optical type, but have been presented with a view to acquainting the experimenter with apparatus of a light -sensitive nature which later will lead to experiments more truly confined to the quasi - optical field.

In last month's issue of RADIO- CRAYT, a simple photoelectric -cell amplifier was described and directions given for its construction. It was also explained how this photoelectric -cell amplifier, with its attendant photoelectric -cell, could be used to change variations of light (from a flashlight) into variations of electrical current (as manifested either visually on a milliammeter or in a loudspeaker in the form of sound). The frequency of the sound was dependent upon the number of times the light source was inter- rupted by some such device as the blades of an electric fan, etc.

Now, in this month's department it will be shown how, with the aid of another piece of apparatus which may readily be built, it is possible to translate the recordings on a


Schematic circuit of the amplifier suggested by Mr. Brennan.




BOOK REVIEW N. R.I. FUNDAMENTAL RADIO COURSE The fundamental radio course offered by the Na-

tional Radio Institute for home study comprises a

series of thirty -five booklets of unusual complete- ness. They start with an elementary explanation of electricity and finish with a description of a typical broadcasting station. The course is of value both to rank beginners and "practical" radio men who just picked up their knowledge haphazardly.

The individual booklets are reviewed herewith:

1 FR: A Bird's Eye View of Radio: The elementary basis of radio. which includes the nature of electricity and magnetism; sound and radio waves; the transmission of such waves through space and the elements of radio receivers are discussed to give the student the background of the radio industry.

2 FR: The Language of Radiotriciana: The language consists of signs, symbols, blue -prints. tables of figures and graphs. In this book the nature of these parts of this silent language is explained by numerous examples.

3 FR: Practical Radio Circuits: Beginning with the simplest type of electrical circuit, progress is made toward more advanced circuits, and finally a set of progressively complicated radio circuits is drawn and explained.

4 FR: How The Radio Receiver. is Supplied With Power: Radio sets need power in order to operate. The various sources of power arè described, their principles of operation explained and the various types and uses analyzed.

5 FR: How Resistors Are Used In Radio to Control Current Flow: As a means of regulat- ing the current in radio circuits, resistances are very important. The uses of resistances, the various types and how resistances are measured in various radio circuits, are described.

6 FR: Radio Coils -Why and How They Work: The second requirement in a radio circuit- inductance -is obtained, as this book will chow, by the use of coils of wire. The theory of inductance, the calculation of inductances and their use in radio circuits are described.

7 FR: Radio Condensers -Their Function and Operation: The third necessity for a radio circuit, capacity, is obtained by the use of a variety of condensers. The theory and operation of condensers are explained in this book.

8 FRI: How a Vacuum Tube Works -Types of Vacuum Tubes in Use: The vacuum tube is the wonder product of the 20th century. In this book the operation of vacuum tubes and their importance to radio operation are discussed for the newcomer to radio.

9 FRI: Radio Transformers and the Prin- ciples of Tuning: The nature, use and construction of transformers are explained in this book as well as their uses in tuning radio circuits. The method of calculating reactance. impedance and the obtaining of resonance are also explained.

10 FRI: How A Three -Element Tube Am- plifies: This book returns to a more detailed study of the theory and operation of modern vacuum tubes. their characteristics and how calculations are made on their operation.

11 FRI: Iron. Core A. F. and Power Trans- formera: The elements of a magnetic circuit: how iron cores are magnetized and used in transformers ; the characteristics of transformers and their application to radio as audio frequency transformers are carefully described in this book.

12 FR1: How a Two- Element Tube Rectifies A. C. in Power Pack Operation: The vacuum tube is necessary in a radio circuit as a means of changing alternating to direct current. A detailed 'study of the vacuum tube as rectifier and some of its ingenious uses and characteristics are explained in this book.

14 FR: Changing Sound Into Electricity and Electricity Into Sound: The basis of radio, as well as talking pictures, the telephone. etc., is the conversion of sound energy into electrical energy and vice versa. The nature and peculiarities of sound and its application to microphone: and sound reproducers are covered in this book.

15 FR: The Triode ea an Audio Amplifier: The triode is a three -element vacuum tube; it plays a most important function in radio, talking pictures and telephones as an amplifier. The characteristics, use and importance of audio amplifiers are thoroughly explained.

16 FR: The Vacuum Tube in Radio Frequency Stages: The sensitivity of a radio receiver depends upon the radio frequency amplifier tubes.


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NOW, EVEN BETTER! RECENT tube developments have

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362

RC-I2

A REMOTE -CONTROL TUNING SYSTEM (Continued front page 337)

electromagnets from bells or buzzers with their original windings. Both Ml and M2 are fastened to the base with angle irons and connected in series. The armature consists of two lengths of iron about 2 inches long by 1_. -inch wide. These are fastened to a strip of hard rubber about 3% inches long and approximately 14 -inch wide. A hole is bored approximately 114 inches from each end of the strip, and a length of brass tube, % -inch in diameter and 2 inches long, is forced into the holes. A set -screw in the hard rubber holds them in place.

Two spring clips are soldered on each tube and bent as shown in the diagram and photograph. Two lengths of brass rod are mounted by brackets on each end and acts as tracks. Tubing, sliding over these rods, should be a loose fit and not bind. Clips CL2 and CL4 travel the entire length of the blade; but those marked CL1 and CL3 disengage. The sizes and dimensions amount to very little in this piece of apparatus; as it can be seen that when power is applied to Ml, the armature is attracted and slides along rods, thus engaging the clips in CLl and CL3. This provides the circuit for applying power to the driving motor and starting same; while the filaments of the receiver are lighted. Power to M2 causes the armature to reverse its action, and the entire power is cut off. These are actuated by the Circuit Breaker Unit as described above.

The layman may use a flexible cable soldered to the tubing in place of CL2 and CL4; but the spring action of these clips hold the armature in place and prevent closing or opening by vibration or any other causes than by an electromotive force itself.

Tuning Control Unit This unit consists of n steel shaft % -inch

in diameter within a pivot bearing which should swing easily; and should be equipped with a rubber tired pulley. It is located between two, double electromagnets of the buzzer type with their original winding.. Fig. 3 shows this unit in full. Two sets of flat -faced pulley wheels are adjusted to rotate easily by the use of adjustable hangers with bearings. The motor drives one set by the use of a chain drive, while other set rotates in the opposite direction duc to the crossed belt.

It can be seen that power applied to M1 causes the steel shaft to be attracted, and a rubber -tired pulley to engage the face of the rotating flat -faced pulley, thereby causing the shaft to revolve. And through the various worm and spur gears, cause rotation of the tuning variable condenser in one direction. When the power is released, the rubber tired pulley -by reason of centrifugal action -very quickly disengages itself. Power applied to magnets M2 reverses this action ; and due to the rotation of the flat pulley in the opposite direction caused by the cross belt. the shaft now revolves in a clockwise direction. The tuning condenser is operating in reverse.

It will be noted that the grooved pulleys carrying the belt are not of the same size. When the condenser is rotating from the minimum to maximum it is very slow, or vernier, in action. From maximum to minimum, it is very much quicker, but still capable of properly tuning in any station on the return. The reducing gear is of little importance and should have a ratio in the neighborhood of 10 to 1. Slow motion of the tuning condenser is governed mostly by the 16 and 32 pitch worm gears.

The reducing gear is mainly to provide a method by which the pivot shaft can swing easily, and at same time be engaged in mesh without binding. A flexible piece of rubber tubing might answer the purpose and be coupled directly on the worm gear shaft. However, rubber breaks in time and there is always a backlash when it is used.

The pivot bearing holding the shaft is, likewise, of little importance, but it must swing freely. Good types of bearings for this purpose -also for the sliding bearing -are the panel lugs from old telephone jacks. They have a 1: -inch hold and sufficient stock to permit countersinking slightly for the pivot lugs; and in case of the sliding bearing, to permit a slight groove on the axis to accommodate the Bearing Guide.

This bearing guide is used to prevent "wobbulation" in the main, drive shaft.

Magnets should be well fastened to a base - hoard and a clearance of 'Is -inch between each set and the steel shaft at neutral is maintained. In the "miniature" machine shop, adjustable bearing -hangers were used as they eliminate undue fuss in lining up the shafts to prevent binding. (These shafts, pulleys, worm gears, reducing gears, etc., may be purchased at a very low cost from the Plmca MODEL WORKS. TINLON PARK, ILL.)

With regard to the rubber tired engaging pulley, this is a flat type. 11_- inches in diameter, y. -inch face. A heavy rubber band was cemented to the face and is an excellent "gripper" upon the flat -face pulleys. The cross belt may be a length of heavy window shade cord (treated with belt compound); a small spiral Spring connects the ends. This keeps the best taut at all times with no slippage.

The sprocket wheel and chain drive may be eliminated and the motor coupled directly to either shaft. This method of tuning -in stations is far superior to the rotating "cam" methods which are limited only to a selected few. The apparatus constructed by the writer successfully tuned in stations from 10 meters to and above the broadcast band.

Regeneration or Volume Control The regeneration or volume control, shown

in Fig. 4, makes use of the "book" type variable condenser; but may be used equally well with the rotary type variable unit. As will be noted in "section A," when power is applied to the magnets, the armature is attracted, and, acting as a "kicker," on one end of the armature, will strike one or more of the teeth on the ratchet wheel. The length of this stroke is governed by the armature stop. By lengthening or shortening -as the case may be-the ratchet wheel may be governed to move from one to five teeth at each "dot." The backlash stop prevents the ratchet from returning or skipping.

Soldered to the armature movable bearing is an arm of very thin, spring brass carrying a contact point; and located directly over this is an angle arm carrying still another contact point. When the armature is attracted, the arm rises and closes contact. This is of no value outside of providing the necessary oir- cuit lead for shutting off all power when set is discontinued. That is: when button No, 3 is pressed with button No. 2, the Motor and Filament Relays will be in operation: but not unless the circuit breaker, shown in Fig. 4, is closed.

The escapement and pin, as shown In "section B" is exactly similar to that used in all alarm clocks. As the pin travels over the surface to a gradual rise, the pin reaches a point where it drops, perpendicular to the bottom of the beginning of the surface rise. The principle used here is identical. As the ratchet wheel reaches the "falling off" point, the shaft and pin drop back to the original position due to the spring action on the movable leaf of the variable condenser. By the aid of the set -screw on all types of book -leaf variables, it is only necessary to adjust this leaf to the near point of regeneration. It will take in the neighborhood of 14 "dots" to bring condenser from the minimum to maximum; and when maximum is reached, to fall back immediately to the before mentioned position near regeneration.

An exact duplicate is made of this apparatus, except that it is not coupled to a condenser. In place, we install a dial or pointer directly on the shaft. The escapement bevel is filed until both escapements on the variable condenser and remote indicator drop in their respective slots at the same time. If it takes 14 "dote" to obtain the identical procedure with both pieces of apparatus, it stands to reason that when the indicator is connected in series with regenerative control, button No. 3 will operate both in phase.

To adapt the principle of regenerative control to the rotary variable, it is only necessary to loosen the bearings on variable unit so the rotor swings very easily, and couple a "pigtail" connection to the rotor shaft. The escapement tubing, not shaft, is fastened to the rotor shaft of the variable unit in re.

RADIO-CRAFT for DECEMBER, 1932



verse. A spring is fastened to the rotor, but not of sufficient tension to retard the forward motion, but to act as a means to return the condenser to minimum from the maximum. or to the near point of regeneration when the pin falla in a slot. A counter- weight might be installed on the rotary variable condenser to prevent the rotor from returning with a bang.

Tuning Condenser Indicator It is not necessary to go into this phase

very deeply. Locate on the shaft of the variable a length of hard rubber with a fine piece of spring brass at each end. Fig. 5 shows the "works." When the condenser reaches maximum, a contact is closed that operates a

high frequency buzzer. The contact lead of the buzzer "make -and- break" is connected to the remote -control cable running to one leg of the telephone receivers. When the condenser reaches maximum, a high -frequency note will be heard in the receivers, and act as a signal for the operator to let up on button No. 2. Now, when button No. 1 is pressed and held, and the arm comes back to the minimum, another contact is closed, but as

will be noted, there is a resistance in series with the buzzer and battery that cuts down the current through it. and produces a low, or raspy, note instead of the previous high pitch. This is the operator's signal that the minimum condenser setting has been reached.

Schematic Diagram Now that various parts of this apparatu.

are understood, it is our object to observe the action by manipulation of the buttons. Refer to Fig. 6.

First, we press No. 1 and No. 2. A charge is placed in magnet M4; likewise, the circuit breaker magnets M5 and M6 receive a charge as they are in series with MS and M4.

The contacts close at each end and provide a path for local en -rent to charge relay magnet M -1. The armature is attracted and clips engage at F4 and F6 from the action of the clip blades CL1 and CLB. One set, CLS and CL4 start the driving motor, while CL1 and CL2 light filaments.


HOME EXPERIMENTS (Continued front page 360)

phonograph disc into variations of electric current; amplify these currents so they will finally be strong enough to actuate the common, television neon tube, which in turn. has its variations in light intensity changed by means of the photoelectric-cell and amplifier described last month, back into sound as it would come directly from the phonograph record.

It is well to reflect for a moment and re- peat the somewhat complicated processes involved in ultimately obtaining sound from the record.

On the record are the wiggly spiralled grooves representing stored up sound in the form of music or speech. The phono -magnetic pickup unit changes these vibrations into electric current, which is amplified by the resistance amplifier. and then converted into light variations in the neon photoelectric tube. These light variations are then converted back into electric current by means of the photocell, amplified and finally emitted from the loudspeaker in the form of sound.

If it is desired. the experimenter may attempt to connect the output from the detector tube in a radio receiver to the two terminals formerly connected to the phono pickup and in this rather unusual manner reproduce, through the the neon tube, photocell, etc., the radio program being received.

The diagram for the resistance coupled amplifier is shown here. Its construction need not be elaborate. The values of the parts employed are shown directly on the diagram.

Although no practical, permanent results are obtained from this experiment, since sound from the record can be more directly obtained by substituting a loudspeaker for the neon tube, nevertheless this procedure is described so the experimenter will become familiar with the transference of vibration into the current, then into light, then back to electric current and finally into sound.

Next month . confining a beam of light on a target and modulating it by several mechanical means.

ADJUSTABLE SLIDING CLIP

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VOLUME CONTROLS With Interchangeable Switch The new ELECTRAD VOLUME CONTROLS are designed for using a power -switch, when desired, without disturbing control connections. Just snap out the standard end cover and replace with ower- switch assembly. Long ALUM- INUM shafts, also -Casa to cut.

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One of these plugs goes into the tube socket

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Only by resistance testing can you easily and properly with No. 1000 Tester do the following work: Class B Amplification. Muting

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RADIO -CRAFT for DECEMBER. 1932 363



Practical Radio Engineering An opportunity for RADIO MEN to enlarge their scope

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No natter how ouch or how little knowledge of radix you have, there is a distinct nrlvnntage In taking this course. Further detnlls will prove It.

If you wish to specialise in a particular plinse of radio or associated arts. send for a copy of our illustrated ctrtning which contains all particulars about RCA Institutes' various Resident School Courses.

Visit our RCA Institute School in New York or Chicago. You will find them modern, fully - egtdpla'd, and ample in scope for the ever -growing field of radio. We shall be Sind to nee you nt nay time of day- morning. afternoon or evening- from Mondays to Fridays inclusive.

Whether you plan n visit to us, wish to enroll for a resident school class, or merely wish a free cnl'Y of the new RCA Institutes catalog, Sll In and mall the coupon below.

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364

BATTERY -OPERATED P.A. SYSTEM

(Continued from page 331) have a neat job (especially where the hole is cut in the side for the speaker opening). Use white wood and follow the specifications as given. The box may be stained any color (dark oak is very serviceable). Remem- ber, this case must carry the weight of the batteries, so it should be put together very strongly.

Fasten the handle to the top of the case with 8 -32 machine screws and use washers under the nuts so the wood is not weakened by the weight of the completed unit.

The front and rear sides are held in place by the small hooks at the top ; at the bottom there are two brackets with holes which, with the aid of 6 -32 machine screws, form a catch - and -guide holder for the bottom of the remov- able sides.

Iron is used for the amplifier chassis and should be drilled and folded as shown in Fig. 2 and Figs. B and C. There is nothing difficult or new about this chassis, but if the builder wants to obtain the chassis ready -made with all holes drilled as per specifications. he may do so. Follow all dimensions carefully, as the leads from the audio-frequency transformers come out of the bottom of their respective cans, and if the holes are not right, the leads may short to the chassis.

Amplifier Assembly Start the assembly of the amplifier by

mounting the sockets and audio -frequency transformers Nos. 16 and 19 on top of the chassis ; mount the input and output terminal strips on the ends of the chassis ; the input strip to the left, and the output strip to the right.

Wire the filament, plate, and grid connections and after this is finished connect the 4 mf. bypass condenser which is mounted on the wall of the chassis. The input transformer, 7, fastens alongside the 4 mf. unit near the input strip. It might be well to cover the flexible leads of the input transformer with varnished tubing so there will be no short circuits in the input circuit to the grid of the first tube. The secondary has a center -tap connection for use as a push -pull input transformer. Use the two outside wires and be sure that the center tap does not ground. This amplifier should be wired with the idea in mind that no matter what happens. wires must not come loose -solder accordingly.

It will be noted that the assembly and wiring operations are more or less interlinked. This is due to the fact that the amplifier has been made as compact as possible. By wiring the filament and plate leads before completing the assembly, the builder will save lots of trouble and time.

Final Assembly After the ease hardware has been placed in

position and the speaker mounted on the side. obtain some strap iron about 1 -inch in width and bend it into shape as shown in the photographs. These straps are necessary to hold the batteries in place when transporting the unit from place to place. Mount the "C" battery with its mounting bracket in the upper. right-hand side of the box. Place all of the batteries in their proper position and wire them, holding the various wires in place with insulated staples driven into the wooden case. Bolt the amplifier to the chassis in the same manner that was used to hold the sides of the box in place. This permits the easy removal whenever connections to the input or the output terminals must be made.

If the builder desires to have the speaker placed some distance from the amplifier, then the cable running from the output terminal strip must be made longer. In general, do not make this line over 40 feet long and use a wire with as large a diameter as possible- nothing smaller than No. 18.

Operation After the various units have been assembled,

connect the "mike" to the input terminals using terminals marked M and MC for a single button mike, and terminals M, MC and M for two button types. If the phonograph pickup is to be connected, use the terminals marked P.P.

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The better the "mike" the more satisfactory will be the results. Double button "mike?' are to be preferred because of their better frequency response. Microphone current is fixed by the voltage of the single dry cell and this should not be exceeded.

The beat location of the speaker in respect to the mike must be found from experience. In general, keep the microphone as far as possible from the speaker, as there is considerable gain in the amplifier and a strong tendency for acoustic feed -back is present. When the system is used out of doors. this feed -back tendency is more or less reduced. The volume is controlled by the potentiometer mounted on the top of the case. A built-in switch on this control turns the filament voltage on and oft in the zero gain position.

List of Parts One Acratest input terminal strip No. 7148, (1),

(2). (3). (4). (6), (6) One Acratest input transformer No. 2567, (7); One Frost volume control and switch, 80 serin,

600.000 ohms (8) and (27); One four -prong wafer socket, (9) One Acratest carbon resistor, 20,000 ohms, 1

watt, (10) One Acratest carbon resistor, 76.000 ohms, 1

watt, (11) One Acratest carbon resistor, 125,000 ohms. 1





ADAPTERS FOR TEST EQUIPMENT (Continued from page 847)

No. 975, Fig. 18, is for tube tests on PZ, '33, 46 and '47 tubes; used with models 533, 555 and 565 testers.

No. 955G, Fig. 69, is to be inserted in the UY socket of the model 533 tester.

No. 964WE, Fig. 70, is attached to the test plug or 5 -prong adapter for testing the Western Electric 205D tube; used with models 665, 566. 589, 593 and 660 testers.

No. 979WE, Fig. 57. is placed in the UY socket of the tester to test the 205D tubes. Used with 537, 547, 565, 566, 589. 593 and 660 testers.

No. 944WE, Fig. 71. is attached to the test plug of models 537 and 547 testers to test the 205D tube.

No. 999, Fig. 39, is attached to the teat plug so it may be placed in UVI99 sockets; used with models 519, 537. 647, 565, 566, 589, 593 and 660 testers.

No. 429. Fig. 40, is placed in the UX socket of the tester to accommodate the ÚV199 tube; used with all models described for the No. 999.

No. 419X. Fig. 42, is attached to test plugs so it will fit in large UV sockets; may be used with models 519. 537, 547, 565, 566, 589, 593 and 660 testers.

No. 982. Fig. 12. is used with models 533, 555, 565, 593 and 597 testers to check the 82 tube in the '46 socket and the 83 tube in the '71 socket.

No. 965DW is used with models 547, 565, 566. 589, 593 testers and is used for the same purpose as described for Fig. 8.

No. 965KS, Fig. 16, is used to test the 57 and 58 tubes in models 555, 593 and 697 testers. The adapter is placed in the '24 socket.

No. 955G -2, Fig. 17, test the G -2 tube in models 533. 555, 565. 593 and 597 testers.

No. 949K, Fig. 4. tests the Kellogg tube circuits. It is attached to tester plug; used with models 537, 547, 5G5, 566, 589, 599 and 660 testers.

No. 944LS. Fig. 44, is the companion to the No. 949K. It is to be placed in tester socket.

No. 967, Fig. 43, is the large UV -to -UX adapter. It is to be placed in tester socket; used with models 519, 526, 533, 537, 647, 555, 565. 566. 589. 593 and 597 testers.

No. 944JY, Fig. 13, is used with models 533 and 565 testers to test the 2nd plate of the '80 rectifier.

No. 964DS, Fig. 10, makes a 4 -prong test plug from the 6 -prong plug of model 660 tester.

No. 944G, Fig. 72, is used to test the '22 and '32 tubes in models 533. 555, and 593 testers. Place a No. 944G adapter in a UX socket, the tube in a No. 944G adapter and make the control -grid connection. This adapter checks the 865 tube in models 533, 555, 565 and 593 testers.

No. 965CG, Fig. 14, used with models 555. 593, 597 testers to test the 41, 42. PA and PZH tubes.

No. 952J may be used with all Weston testers. Same as described for Fig. 3.

No. 949PT may be used with Weston oscillators and output meters. Same as described for Fig. 19.

No. 954KGL, Fig. 22, is used to test the first section of 93 and 95 tubes; used with models 533, 555 and 565, 593 and 597 testers.

No. 954KG, Fig. 23. tests the second half of 93 and 95 tubes.

No. 944PLCR is for testing the 866 tube in tube checkers. Used with models 533, 556, 565. 593 and 597 testers. Same as described for Fig 24.

No. 955GGKL tests the 5 -prong Wunderlich tube in the '27 socket of 533. 555, 593 and 597 testers. Same as described for Fig. 48.

No. 965GG is for testing 29 and 69 tubes in models 533. 555, 565, 593 and 597 testers. Same as described for Fig. 28.

No. 944BRA, Fig. 29. is used to test the Raytheon Auto Eliminator BR tube. May be used with models 533, 655, 565, 593 and 597 testers.

No. 944BRA is used with the No. 944BRB adapter to test the circuits of the BR tube; used with models 537, 547, 565. 566. 589, 593 and 660 testers. Same as described for Fig. 30.

No. 944BRB, Fig. 31, is placed in the UX socket of any analyzer to test the circuits of the BR tube. This adapter is used in conjunction with the No. 944BRA adapter.

No. 944BHR tests the Raytheon BA and BH tubes in models 633, 555. 665, 593 and 597 testers. Same as described for Fig. 32.

No. 955KPT provides connections for an output meter across a pentode; used with Weston output meters. Same as described for Fig. 33.

No. 955SPT, Fig. 34. same as for the No. 955KPT adapter except for a triple -twin tube.

No. 975KP tests the 7 -prong tube in models 533. 555. 565. 593 and 597 testers. Same as described for Fig. 35.

No. 950HS is the combination adapter having four sockets for testing the 29. 69, 41, 42, 57. 58 and 82 tubes. It later will also be available with a 7 -hole socket. Same as described for Fig. 36.

Adapters for Supreme Testers No. 944F, Fig. 73, is used with models 99A

and 99A +, 400A, 400A +, 400B and 400 -B -3 testers for synchronizing purposes. It permits the connection of a meter in series with the plate circuit.

No. 429. Fig. 40, is used with all Supreme testers. Its purpose is to permit the insertion of a ÚV199 tube in the UX socket of tester.

No. 967. Fig. 43, is similar to the No. 429 adapter except that it is used for large UV tubes such as the 'OOA, '01A, etc.

No. 9541J. Fig. 74. fits the 5 -prong plug of 99A and 400A changing it to a 4 -prong plug.

No. 954, Fig. 58, is similar to the No. 954U adapter with the exception that the cathode is connected to the negative filament.

No. 949K, Fig. 4, used with models 99, 99A +, 400A and 400A+ testers to test overhead Kellogg tubes. It is to be attached to the plug.

No. 944LS. Fig. 44. is similar to the No. 949K adapter except it fits the socket of the tester.

No. 944N, Fig. 75. is used in connection with all Supreme testers and any others having an oscillator. Its purpose is to take the place of the tube when neutralizing.

No. 955N, Fig. 76. is the same as the No. 944N adapter except it is made for 5 -prong tubes.

No. 944JY is the same as described for Fig. 13; used with the model 17, and all others not having a milliammeter in the grid circuit.

No. 955. Fig. 77, is merely a 6 -prong extension for 5 -hole sockets where it is difficult to get the plug; may be used with all models.

No. 999 may be used with all models. Same as described for Fig. 39.

No. 977, Fig. 78. attaches to the test plug of models 90 -1J and 2J series and 40013 -N I

series for pentode testing. No. 976, Fig. 79, is similar to the No. 977

adapter except that it fits the socket of the tester.

No. 975. Fig. 18, is for testing the 33. 46. 47, PZ and GA tubes. Use '27 socket of tester. Used with the models 400B and 19 testers.

No. 965SL, Fig. 80, is used with the models 90- 1 -2 -3 -4 and 6.1. and AAA1 testers for testing the circuits of 57 and 58 tubes. It is to be inserted in the 5 -hole socket of the tester; it. is used with either 946DS2H, 9465S, or 956SS adapters.

No. 965KS, Fig. 16, is for testing the 57 and 58 tubes in the models 19, 40 and AAA1 testers. Insert in 5 -hole socket.

No. 955SC2 is for testing the G -2 tube in the models 19, 40, 400 series and AAA1 testers. Same as Fig. 81 except different value of resistor is used.

No. 965PG. Fig. 25, tests the 41, 42, PA and PZH tubes in a '37 socket. Used with 400 series.

No. 965 -55 tests the 55 and 85 duplex -diode triode tubes. Used with the models 17, 19. 40, 99 series, 400 series and AAA1 testers. Same as described for Fig. 26.

No. 955GGKL tests the Wunderlich 5 -prong tube in '27 sockets. Same as described for Fig. 48.

(Continued on pope 375)


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VOLUME CONTROLS CLAROSTAT Replacement Volume Controls are Custom. Made" to exactly suit the receivers for

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366

D.C. KIT SET (Cou tintied from f ¡Jaye 339)

enam. wire wound on a tube 1 in. in dia. At the factory the inductance of these secondaries is accurately balanced for zero -beat in an oscillator test- circuit, a bakelite finger moving the wire r4 -in., a turn at a time, until a meter gives the correct indication.

Each rotator section of the tuning condenser gang is equipped with two end -plates with adjustable segments: these provisions for alignment are independent of the usual trimmers. which furnish control of the minimum capacity in each section. -a

Two wires along one side of the tuning condenser gang eliminate circuit oscillation due to stray fields. These wires appear in Fig. A.

The antenna lead is separately shielded inside the chassis to prevent circuit oscillation due to over -all coupling. Dual isolation is obtained through the use of condensera C9. CIO: the possibility of grounds is further reduced by the use of long leads for the antenna and ground instead of the more common binding posh: th. negative lead of the power line connects directì> to the chassis, as indicated in the schematic circuit. Fig. 1.

Resistor R71 operates as an R.F. grid suppressor ; it is bypassed by the capacity of the preceding tube. V4. A terminal strip is provided on the rear skirt of the chassis for connecting a phonograph pickup into circuit.

The author will be glad to advise further concerning this kit -set or the completely wired and tested instrument. Just enclose a stamped, return- addressed envelope.

List of Parts One DeJur -Amsco 4-gang variable condenser,

360 mmf., with trimmers, Cl. C2, C3, C4: One Savil Type 748 special shielded R.F. coil kit

(see text for description). Ll to L4; One Micamold fixed condenser, 250 mmf., C9; Nine Cosmic fixed condensers, 0.1 -mf., C10 to

C18. and C23: One Micamold 100 mmf. fixed condenser. C19; One Cosmic fixed condenser, .01 -mf., C20; One Cosmic fixed condenser, 0.5 -mf., C21; One Cosmic fixed condenser..05 -mf., C22: One Solar non -polarized dry electrolytic con-

denser, C24: One Centralab volume control potentiometer,

min. renia, 175 ohms, total 10.000 ohms. RI; One Centralab tone control, 0- t/4 -meg., R2; One I.R.C. Durham carbon resistor. 15.000 ohms,

R3: One I.R.C. Durham carbon resistor, 200 ohms.

R4; Two I.R.C. Durham carbon resistors, 600 ohms.

R5, R6; Two I.R.C. Durham carbon resistors. 50.000

ohms, R7. R8: Three I.R.C. Durham carbon resistors, 1. meg..

R9, R10. R12: One I.R.C. Durham carbon resistor. x / -meg.,

R11; One I.R.C. Durham carbon resistor, 2,000 ohms,

R13; Two Perry No. 3 coated. 20 -watt resistor. R14

180 ohms. R15 240 ohms; One Magnavox type 154 special, dynamic repro-

ducer; field coil 75 ohms ; built -in output transformer T2 primary matches the push - pull 48's

One Amertran type AF -8 input transformer. T1; One Stancor 25 hy. choke of 50 ma. rating, CH.; Four Aluminum Goods Co. of America tube

shield cans for VI to V4: One DeJur-Amsco flying -spot tuning dial; Three RCA Radiotron type 239 tubes, V1. V2,

V3: One RCA Radiotron type 236 tube. V4: One RCA Radiotron type 237 tube, V5: Two RCA Radiotron type 48 tubes. V6, V7; One 6 V. pilot light. 0.15 -A., V8; Five Micarta Fabricators 5 -prong sub -panel

type sockets, for VI, V2, V3, V4. V5; Two 6 -prong Micarta Fabricators 6 -prong sub-

panel type sockets, for V6, V7; One Micarta Fabricators 4 -prong sub -panel type

socket. for reproducer cable plug; One Eby twin -type binding post strip, for phono.

pickup; One Elan aluminum chassis, 1 /16 -in. thick and

8sfix13tx3 ins. high: Three Kurz -Kasch brown bakelite knobs. for

controls: One Savil midget cabinet, type 748 Special.

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A NEW 2 -VOLT SUPERHETERODYNE (Continued front page 340)

mounted on the front chassis wall. Switch 48 in series with the chassis and the "A" minus socket terminal 47, is an integral part of the volume control. Transformer 39 is mounted on the side wall and the eight Am- perites are also mounted on the side walls, as shown in Fig. B.

The R.F. choke, 34. the fixed resistors, and the cartridge -type condensers are all fastened in place during the process of wiring, being soldered as close as possible to the parts with which they function. The "C" battery is mounted beneath the chassis in the rear corner. being held in place by a to in. brass strap; in order to more clearly show the position of each component, the battery was not connected into position when the underside view. Fig. B. was taken.

The two coils 2 and 12 are mounted last, two mounting holes being required for each coil. Before coil 12 is mounted, it must be

altered in order to serve as an oscillator. Re- move the two turns of silk- covered wire and also disconnect the primary (the coil wound on a piece of wood within the fiber form). This is done by unsoldering the connections at the terminals marked "P" and "B." Next, wind about 25 turns of No. 36 enamelled wire on the end of the coil nearest the terminals. soldering the lower end of this new coil to the "P" terminal and the upper end to the "B" terminal. This winding is used as the plate coil.

Then take off about 36 turns from the grid end (top) of the winding on the fiber form. This will leave a coil about 13/16 inch in length. Resolder the end of this coil to the "G" terminal. These turns are removed so that condenser 13 will track with condenser 4. For exact tracking, a few more or less turns may be required and this must be determined by experiment after the set is in operation. All tests should be made with the coil shields in place. After all adjustments have been completed, the coil shields are permanently soldered to the coil bases.

The set is now ready for wiring. The filaments are wired in first. leads next, the bypass condensers, and, finally. all plate leads. For tone control. substitute an Electrad RI -203 potentiometer for the fixed resistor at 37. Connect the movable arm to one end of an .02 -mt. cartridge condenser. with the other end of the condenser grounded to the chassis. Be sure to peak the I.F. transformers at 465 kc. The writer will be glad to advise further concerning the components. etc.. used in this superheterodyne.

Top and bottom layouts for this receiver may be obtained from the writer by enclosing 5c to cover mailing coats.

List of Parts Two Cardwell "Midway" type 407 -B variable

condensers. 365 mmf.. 4. 13; One Electrad volume -control potentiometer,

100,000 ohms, type RI- 242 -P, 26, with switch, 48;

One Electrad tone -control potentiometer, type RI -203, 37, to be substituted for fixed resistor (see constructional directions);

Three Automatic Winding Company 465 kc. I.F. transformers, complete with I.F. coils, tuning condensers and shields, 17, 21, 29;

One Automatic Winding Company shielded antenna coil, 2;

One Automatic Winding Company shielded R.F. coil Isee directions for using this as oscillator coil). 12;

Two Aerovox mica condensers, type 1450, 150 mmf., 6. 14;

One Aerovox mica condenser, type 1450, 100 mmf., 7;

One Aerovox mica condenser, type 1450, .001 -mf., 33;

Five Aerovox cartridge condensers, type 281, .02 -mf., 9, 10, 19. 23, 31;

One Aerovox cartridge condenser, .05 -mf., type 281, 36;

One Trutest R.F. choke, type 211 10214. 34; One Trutest push -pull input transformer, type

2C1651, 39; Six Trutest 4 -prong wafer -type sockets, 8,

16, 20, 24. 32. 38 Two Trutest 5 -prong wafer -type sockets, 40,

41;

NEW TUBES (Continued front page 335)

the bias is established across the grid leak. This decrease in effective bias voltage causes an increase in plate current which in turn raises the grid current and increases the opposing drop. This effect is cumulative, and in some circuits may reach such proportions as to damage the tube and even result in destruction.

The conditions just described will not be encountered if a grid choke with a low D.C. re- sthtance is employed in place of a grid leak. Of course, this tube may be operated either alone. two in parallel, or two in a push -pull connection. A standard four -prong socket is used and the curves given in Figs. 5 and 6 are especially useful.

The following characteristics obtain when used as a class A amplifier: Filament voltage, 7.5; plate voltage, 350 to 425; grid bias, -72 to -100; load resistance. 5,000 to 8,000 ohms; amplification factor, 3; plate resistance, 2,400 to 2; 500 ohms ; mutual conductance, 1,250 to 1,200 micromhos; plate current 34 to 28 ma.; peak permissible grid swing. 68 to 96 volts; undistorted output power, 2.1 to 3 watts.

The following ratings obtain when used as a modulator: Maximum plate voltage, 425: maximum plate dissipation, 12 watts: grid bias, -101 volts; modulation factor .68: D.C. plate current, 25 ma.: peak grid swing. 97 ; oscillator input per modulator tube, 14 watts.

The curves given in Fig. 6 should be especially useful for the transmitter amateur in the process of designing a 'phone transmitter.

The 59 Power Output Pentode In the October issue of RADIO -CRAFT the

author described a new universal automotive output tube capable of being operated either as a class A triode. a class A power-output pentode, or as a class B power- output triode. this tube being known as the 89. In this issue, we described its companion tube in the 21/2-volt line known as the 59. For details concerning the connections of the grid in order to secure any of the classes of operation mentioned above, the author suggests that the readers refer to the October issue of RADIO- CRAFT.


One Trutest 6 -prong wafer -type socket for power connections 45, 46, 47, 50, 51, 52;

One Trutest 6 -prong plug for making cable connection with 6 -prong socket;

Two Trutest binding posts, 1, 3; Two Trutest bakelite vernier dials, type

2119803; One 221/2 volt "C" battery with 161/2 volt tap.

42, 43, 44; Three 45 -volt "B" batteries; Six amperites. No. 632, with mountings, 8A,

16A, 20A, 24A, 32A. 3SA; Two amperites, No. 633, with mountings,

40A, 41A; One I.R.C. (Durham) 15,000 -ohm metallized

resistor. %-watt, type F -1, 25; Two I.R.C. (Durham) 30,000 -ohm metallized

resistors, 1/2-watt, type F -' 11. 27; Two I.R.C. (Durham) 50,000 -ohm metallized

resistors, 1/2-watt, type F -%, 18, 22; One I.R.C. (Durham) 50,000 -ohm metallized

resistor, 1 watt, type F -1, 30; One I.R.C. (Durham) 60.000 -ohm metallized

resistor, 1 -watt, type F -%. 28; One I.R.C. (Durham) 100.000 -ohm metallized

resistor, 1 -watt, type F -Ií. 15; One I.R.C. (Durham) 150,000 -ohm metallized

resistor, 1 watt, type F -1, 35; One I.R.C. (Durham) 600,000 -ohm metallized

resistor, type F -1, 1 watt, 37; One I.R.C. (Durham) 1 meg. metallized re-

sistor, 1/ -watt, type F -s /_, 5; Three type 130 2 -V. tubes, 16. 32, 38; One type 132 2 -V. screen -grid tube, 8; Two type 134 2 -V, variable -mu pentode tubes,

20, 24; Two type 133 2 -V. output pentode tubes, 40,

41; One roll Corwico braidite stranded hook -up

wire; One Corwico battery cable, six wire, No. 231; One Blan aluminum chassis, 1 /16th in. thick,

7 x 12 x 31/2 ins. high; One 1/2-amp. Instrument Littelfuse. No. 1004; One Littelfuse Gryp Connector. No. 1039; One Magnavox No. 254 permanent magnet

speaker with push -pull output transformer to match type 133 output tubes.


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367



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Full details about the OFFICIAL REFRIGER- ATION SERVICE MANUAL will be found on Page 377 of this bane. Turn to the announcement NOW.

368

OPERATING NOTES 3 New 5Oc Books (Continued frulla paye 349)

service department, and they advised the lady that a condenser was "shot" and that it would have to be replaced. They did. ( I) and returned the machine to her together with a bill for $15.00. When it was placed in service again it was in the same condition as before.

We were then called in to service the instrument and the first thing we did was to turn on the set. All tubes were checked and found O.K.; likewise all voltages were O.K., however, after waiting about half an hour p -1-o -p and no reception. The tubes were again examined and it was found that all filaments were lighted but that there was no plate voltage on any of the tubes whatever. There was, however, a slight excess plate voltage on the leads from the '80 rectifier. The set was then brought to our shop for examination.

Our tests showed that the trouble was in the aluminum can that housed the power transformer and the filter chokes; because after the leads had been disconnected the condensers and the resistor all checked O.K. In other words. this appeared to be just one of those things. An examination of this can revealed that the transformer and double choke had been dropped in haphazardly and then filled with compound. Naturally when it was heated after the set had been in operation for about 20 minutes. any vibration whatever would cause the chokes to drop down and touch the high voltage terminal. As soon as the set was turned off the contrac- tion of the mass of compound would open this contact and the machine would operate until sufficient heat was generated to soften the compound allowing the chokes to sink. at which time it would cease operating.

We opened the can in question instead of replacing it (the lady was pretty well disgusted with the machine after the so- called service she had received). heated the unit in an oven until the compound ran and then insulated the chokes and transformer from the aide of the can and from the high voltage terminal.

STATEMENT OF THE OWNERSHIP. MANAGEMENT, CIRCULATION. ETC.. REQUIRED BY THE ACT

OF CONGRESS OF AUGUST 24, 1912.

Of Radio- Craft. published monthly at :alt. Morris, Ill_ for October 1. 1532.

State of New York Ì. County of New York(ss.

Before me. a Notary Public In and for the State and tounly aforesaid. personally apiIeareal Irving S. Manhelmer, who. having been duly sworn according to law. deposes and says that he Is the business manager of the Radio-/'raft and that the following is. to the best of his knowledge and belief. a true statement of the ownership. management and if a daily paper. the circulation). etc.. of the aforesaid pull l^at Ion for the date shown in the above caption. required by the Act d August IL 1912. embodied In section 411. Postal

Laws and Regulations, printed on the reverse of this form, to wit:

L That the names and addresses of the publisher, editor. managing etlitar. and business managers are: Publisher. Teehni. Craft Publishing Corp.. 404 North tvcsley Ave.. Mt. Morris. 111. : Editor llugo Gernsback, 98 Park Place, New York Citi: Managing Editor. 1.ruls Martin. 98 Park ('lare, New York City; Business Man- agers, Irving S. Manhelmer. 98 Park Place, New York l'Iq'.

2. That the owner la: (If caned by corporation. its name and address must be stated and also immediately thereunder the names and addresses of stork- holders owning or holding one per rent or more of total amount of stack. If not owned by a corporation. the names and addresses of the individual owners must be given. If owned by a firm. nnopany. or other unln-

rporated concern. Its name and address. as well as those of each individual member, st be given.) Technl -Prsit full ishine Corp.. 404 North Wesley Ave.. Mt. Morris, III. ; Hugo Gernsback. 98 l'arc Place, New York City: Sidney Gernsback. 95 Park ('lace. New York City: 1). Manhelmer, 98 l'arc Flare. New York City.

3. That the known bondholders, mortgagees., and other security holders owning or holding 1 per sent or snore of total of Anode- mortgages, or other securities are: (If there there era none. so state. ) None.

4. That the two paragraphs next above. giving the names of the owners, stockholders,

list and security ladders.

If any. contain not only the lint of stockholders and eceurlty holsters as they appear upon the hooks of the mnpany but also. in rases where the tuler or

security bolder appears upon the hooks of the mnpa as trustee or in any other fiduciary relation. the name of the person or corporation for whom such trustee H acting. Is alven; also that the said two paragraphs contain statements embracing sCant's full knowledge and ballet as to the circumstances and conditions under which stockholders and security holders who do not appear upon the hanks of the company as trustees, hold stock and securities in rapacity other than that of hunt aie owner ; and this amant has no reason to believe that any other person. ssrlatlon. or corporation has any interest direct or indirect in the said stock, bonds, or other securities than as so stated by him.

I. S. MANIIEIMER. Business Manager.

Sworn to and subscribed before me this 26th day of September. 1932. (Seal) JOSEPH 11. KRAUS.

Notary Public. (il) commission expires Mar. 30, 1933.)

No. I.

FORMULAS AND RECIPES

For the Practical Man

By S. GERNSBACK

An extremely helpful book showing you how to save money by making in your own home, at a frac- tion of the regular cost, the hundred and one prepara- tions which you now buy for use at home or business.

PARTIAL CONTENTS: . Adhesives: Glue . Cements. 2. Cleansing: Stain Re-

movers. Bleaches. 3. Metal Craft Coloring, Oxydicing. Plating Polishes. 4. faintis Colors. Stains. Val nishea. 5. Glass-Working: Cutting, Drilling. Boring, Etching, Engraving. 6. Rood- ('raft: Fireproofing, Acid-proofing. Waterproofing. Furniture Polishes. 7. Irks: Sympathetic. olsible, lleetograph. 8. Photography: Developers. Emul- sions. Fixers. 9. Antidotes for Poisons. Remedies for Burls and Scalds. Disinfectants. 10. Preparation. Mnipulation. Handling. Mixing. Tables of Weights and Measures. Useful Tables.

No. 2. FUNDAMENTAL PRINCIPLES OF RADIO Radio Simply Explained -Its Origin, Natura

and Functions By LOUIS MARTIN

Prepared with special consideration given to young members in the radio pro- fession, and those who have gained their experience in a haphazard fashion. This radio primer is a handy fundamental aid for "checking up" and systematizing your knowledge of radio. Re- gard:ess of how much you know about the subject, you should read this book.

PARTIAL CONTENTS: Chapter I- Fundamentals of Radio: Electricity. Resis- tance. Batteries. The Magnetic Circuit. The Magnetic Field. Inductance. Contien.ers, A.C. Circuits, Propaga- tion of Radio Waves; Chapter 11 -The Simple Radio Set. Single. Two. and Three -Circuit Turners. 'Elie flattery Set. Vacuum Tubes, Electric Seta, Loud Speakers: Chapter 111 -Diagrams. How to Read Them; Chapter IV -- Amateurs and Itroadeast Stations. Talking Pictures. Television.

No. 3. ELEMENTARY MATHEMATICS for the Technician and Craftsman

By C. SHAINMARK

This manual has been especially prepared for the man who wishes to acquire a working knowledge of the elementary principles of mathematics. A complete treatment of the subject is given by the author. Mr. C. Shainmark, with special attention to the use of mathe- 'matics in Radio and other technical work for those who employ its formulas daily.

PARTIAL CONTENTS: -Arithmetic: Addition. Multiplication. Subtraction, Di-

vision, How to Use Decimals ; 11- Fractions. Percent- Keg, Ratio sod Proportions ; III- l'oavers ami Roots; V -The Metric System; V -How to Measure Surfaces nil Volumes; VI- Mathematics for the Manual and

Technical Craftsman; Vu -Special Mathematics for the tallo Technician; VIII -Commercial Calculations, Short -

mut Arithmetic, Interest Calculations. Dismounts; IX- Weights and Measures ; X- l'seful Tables.

All our books are of uniform size, 6 x 9 inches, and contain 64 pages. The books are printed on strong paper with stiff colored covers.

PRESS GUILD INC., IS Murray St,New York,N.Y.,RC-12 Enclosed find 4.... __for silo II tiail use postpaid

the following books:

No. 1 No. 2 0 No. 3

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A MUTUAL CONDUCTANCE METER (Continued from page 341)

alternating voltage is applied, secured . by a voltage divider across the usual 60 cycle, A. C. line. In the plate circuit, the alternating current resulting from the A. C. on the grid is measured by means of the rectifying unit and D. C. meter. A resistor is used to supply a path to the plate for the D. C. in the circuit, which is blocked from the meter by a 2 mf. condenser. Thus, regardless of the D. C. value of the plate current, the meter will not read until A. C. is applied to the Arid, and the reading, regardless of the type of tube, will be solely dependent on the mutual conductance.

The complete design is indicated in Fig. 2. Resistors RI, R3, and R4, with the rheostat R2, form the input circuit. Resistors R5 and R6 in the plate circuit form a path for the D. C. plate current; R5 being used for power tubes with low plate resistance while R6 .e used for all other tubes. The miniature, copper -oxide rectifier and meter are connected in series with the input resistors (terminale 9 and 11 to terminals 1 and 2) to adjust for line -voltage variations; and, to read mutual conductance, are connected with the blocking condenser, across either R5 or R6, depending on the type of tube under test. The key switch SW.1 when in a neutral position, connects the meter and rectifier in the input circuit and the line voltage may be adjusted.

When thrown to the right, the meter and rectifier are transferred to the plate circuit; and, with the condenser in series, are shunted across R6. With the toggle switch SW.2 also thrown to the right, mutual conductance of all tubes which have no control -grid cap, other than the 8- element power tubes. may be read. With the toggle switch SW.2 thrown to the left, SW.1 remaining as above, all tubes with a control -grid cap may be tested. With SW.1 thrown to the left, the toggle switch is out of the circuit and the meter is adapted to testing 3- element power tubes.

The condensers C2, C8, and C4, and the switch SW.3 are needed only when the tester is used in the field. They serve as by passes for circuit elements in the radio set. The switch SW.3 is closed when testing power tubes and connects the cathode terminal to the center tap of the filament shunt resistor which is across the filament supply terminals of the power tube.

The resistors. RI, R3, and R4, should be of 1 -watt rating. and preferably wire -wound. R3 and R4 should be accurate to within 1 per cent; R2 may be any good volume control of 100,000 to 200,000 ohms resistance; R5 and R6 are heavy -duty, wire -wound resistors. 50 watt rating; the 2 mf. condenser Cl should be of high quality with no leakage. The voltage across it is small, but to ensure no leakage, it is better to use a 800 -volt condenser at this point. Condenser C2 should be a high voltage electrolytic; CS and C4 need only have a 160- volt rating.

The miniature copper -oxide rectifier is a Tau -rex; the meter, a Weston 0-1. ma. (the one shown in the photograph is the galvanometer from a thermo-galvanometer which had its thermo- couple removed and has been shunted to give a full scale deflection for 1.ma. D. C.).

If an accurate 0 -10 ma., A.C. meter is available, the calibrating of the meter may be done as shown in Fig. 3. If not, tabulated calibration points are given below:

micromhos scale divisions (D.C.) 400 9 600 19 800 30

1000 40 1200 61 1400 64 1600 75 1800 87 2000 98

Construction Details The meter should be removed from its case

and the dial taken off, being careful not to touch the pointer, and the printing immediately above the dial scale should be removed by rubbing same with a dampened eraser. The calibration may be marked in, using a fine pen and india ink. Replace the dial, and put the meter back in its case, taking particular care that the zero adjustment notch fits in its proper place.

The apparatus may now be assembled and wired. A 7x10 in. bakelite panel is used. The terminal block shown in Fig. 2 was taken from a discarded Radiola radio- record switch; a binding post strip, however, may be substituted. If there is any difficulty in obtaining the key switch, SW.1, the switches A and B, Yaxley D. P. D. T.. (also shown in Fig. 2), may be substituted. Switch A may be a push- button type as it is used for line -voltage adjustment only. For service work, condensers C2, C3, and C4, and switch SW.3 are needed. The condensers may be mounted in the box containing the apparatus. SW.3 should be mounted on the panel. An analyzer plug with 6 prongs, adapters for 4- and 5 -prong sockets, and a 7 -wire cable are also needed for service work.

For screen -grid tubes, the applied A.C. grid voltage is 1.2 (R.M.S.). For all other tubes, except 3- element power tubes, the applied A.C. grid voltage is 10 per cent higher, or 1.32 (R.M.S.), to compensate for the plate circuit load. For 3- element power tubes, the applied A.C. grid voltage is 5.5 (R.M.S.). These voltages are simply and accurately determined by adjustment of the rheostat R2 with the key switch in neutral position, which connects the meter and rectifier in series with the A.C. line. With 100,000 ohms in series, this meter will give a full -scale deflection for 117 volts A.C. Therefore, the current through the rectifier at this voltage is 1.17 ma. The portion of the voltage divider furnishing the applied grid voltages R3 and R4, have a combined resistance of 5,250 ohms. Therefore, if we adjust the rheostat. R2. until 1.06 ma. A.C. is flowing through R3 and R4, the voltage drop across R3 and 114 will be 5.5; across R4 alone, the drop will be 1.8 volts. Thus. with a single adjustment, we have the proper test voltages for all types of tubes other than screen -grids with a control -grid cap. For the latter, the setting required is 10 per cent lower as no compensation is necessary due to the high plate resistance of this type of tube. Since the meter reads 100 when 1.17 ma. A.C. is passing through the rectifier, it will read 1.05/1.17 of 100 or 90 when 1.05 ma. A.C. is in the circuit. So we therefore adjust the meter to read 90, by means of the rheostat, except for tubes with the control -grid cap, for which we adjust the meter to read 10 per cent lower, or 81.

Some power tubes have a mutual conductance greater than 2,000, and as our scale extends only to 2,000, provision must be made for testing these tubes also. However, this is very simply done. If we reduce our input voltage by one -half, we may double the mutual conductance readings indicated on the meter. Therefore, if the meter goes off scale on any tube. readjust the line voltage setting until the meter reads 45 and double the indicated mutual conductance reading.

It is easy to remember what the mutual conductance of new tubes of various types should be. The '27, '26, '24, and '35, will all average around 1,000 micromhos. Power tubes, such as the '71A, '45, '50, will read around 1,800 or 2,000, while power pentodes will read slightly higher. Battery type tubes, such as the 'OIA, '99, '12, will read around 600 to 800, with the '22 type still lower. Tubes should be replaced if their mutual conductance has dropped to 8 or ',4 of these values. In R.F. stages, even a 10 per cent drop makes an appreciable difference, especially when there is some regeneration present.

This tester may also be used as a tube voltmeter for measuring voltages by simply putting a tube in one of the test sockets and connecting the unknown voltage in series with the grid. The mutual conductance of the tube is first measured in the usual manner; then the applied A. C. teat voltage is removed from the grid. The mutual conductance reading has indicated the reading to be expected for a known input voltage. The unknown voltage is therefore greater or less than the mutual conductance reading depending upon the ratio of the indicated mutual conductance with the unknown voltage applied to that of the reading with the known applied voltage. The tube selected for this purpose should have a normal operating grid bias well in excess of the peak voltage to be measured.


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LOUDSPEAKER FACTS (C",, t i tu(ed from page 342)

then the baffle length is infinite. Therefore, if the loudspeaker and amplifier are capable of supplying down to the lowest transmitted frequency, the baffle will also reproduce this frequency. Under such ideal conditions we would indeed have an ideal sounding system.

Reverberation and echo will spoil the best sounding system. Reverberation is also known as "Multiple Reflection," and is the reflection of the sound from walls, ceiling and floor. gradu- ally losing a little energy at. each reflection until ultimately the sound dies out to inaudibility. The time that it takes for a given signal to completely die out is the duration of audibility of the reverberation. The rate at which reverberation disappears is proportional to the rate at which sound is absorbed, and thus all substances have different relative absorbing powers.

Echo, on the other hand. is a special case wherein a short, sharp sound is distinctly repeated by reflection, either once from a single surface, or several times from two or more surfaces.

There is still another condition which produces resonance and is the result of the emanating sound producing vibration in objects whose fundamental period of vibration is excited by the sound and therefore goes into continued vibration. Such a phenomenon can produce a most exasperating sound. for the guilty object is oftentimes exceedingly difficult to locate.

Determining Loudspeaker Position The position of the speaker on the wall is

of vital importance; likewise is the method of sound distribution, or rather the type of mounting that will be used with the speaker. The distribution of sound can be likened to the distribution of light, and if a source of light is placed in a position corresponding to the focal point of the loudspeaker, then the angle of the light beam can be taken as a visual indication of how the sound waves emanating from the loudspeaker will disperse throughout the room.

First, the angles of distribution must be obtained by using a searchlight with a variable focus attachment, and. by holding the light in an approximate location for the loudspeaker and varying the focal length, the light will cover the entire room (Fig. 1B). A definite angle will be found that will easily cover the major portion of the room. This angle must be measured and will be the horizontal distribution angle. (Of course the only light in the room while these measurements are being made will be due to the searchlight.)

Second, the floor angle, Fig. 1C, must be obtained: and this is perhaps the most important measurement to be made, as this angle will also take into consideration the true height above the floor that the speaker must be placed. If the speaker is installed near the ceiling on the 20- foot wall and designed with the idea of only covering the horizontal angle of distribution, then there will be an almost complete dead spot directly below the loudspeaker on the floor as shown in Fig. 1D.

The floor angle must therefore be accurately determined so as to cover that position nearest the wall under the loudspeaker where sound will he required. The usual method of measuring this angle is to use a ladder and flashlight. and by striking a balance between that point where the horizontal distribution can cover its terri- tory without blasting those in the front, and where the floor angle drops down and delivers its sound to the desired front location. Some also consider the ceiling angle, especially where the ceiling is constructed with highly reflective material. In such a condition, the ceiling angle is usually designed with a flat, horizontal angle the idea being to keep the sound from being projected against the ceiling as much as possible.

At least seven or eight separate measurements are made for each angle. The groupings for the individual angles are then averaged and the final three angles thus obtained are plotted on paper. Then, by also laying out the resulting horn to scale, usually known as a "Flare." the distance from the front of the flare to the back can be determined. The limits in the rear of the flare will of course be the section where the outside diameter of the cone just tits.

The ultimate result will be a unit that will work directly into the space that it is designed to cover. In actual practice. it will be found that where rooms are of the same shape. the

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S. GERNSBACK'S RADIO

ENCYCLOPEDIA 2nd EDITION

This Neu' Second Edition gives you an i explanation of every word used in radio.

2,201 RADIO DEFINITIONS 1,253 TECHNICAL ILLUSTRATIONS 2 90

34 TABLES AND CHARTS 24 PAGES OF APPENDIX

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distribution angles will be similar, the greatest factor of discrepancy being the floor angle. Sev- eral manufacturers make flares to fit almost all conditions of sound work and photographs of these are shown here.

It is well to remember that in rooms where there is a tremendous amount of echo and reverberation the best method of sound coverage is to install small speakers all over the room and then to drop the volume so that each speaker will only cover a small area; but due to the fact that the volume is at such a low level, the sound will only be able to cover its own area and then fade out. The usual argument against the use of many speakers is that one speaker will overlap the other resulting in the listener hearing the signal from more than one direction, creating the feeling of a bad echo. This argument is true but it is only true where the level is raised so that overlapping points will result. It is not true where the level is adjusted to a low value that will only cover a predetermined area. The best results will be obtained where the ceiling can be opened and speakers inserted with the sound coming down and covering the desired area. In any case, it is much better than having one or two large speakers operating at high volume to cover a room. and then not being able to understand a word due to the preponder- ance of echo and reverberation.

Where a room is acoustically correct and can be fed by the type of unit described before, by all means use the large type speaker. The ex- cellence in tone quality will more than repay the installation of such units.

In many large public places it is often necessary to prevent the sound that is being fed to one room from being heard in the adjoining room. Oftentimes the loudspeaker will feed a room and the back of the speaker will be in a second room where it is vitally important that the back wave should not create any disturbance.

The only thing to do in such a condition is to install the speaker and flare in a well padded box. The idea of completely enclosing the entire back of the speaker in a padded box might appear at first to be extremely poor practice. Ac- tually, with the proper precautions. excellent sound can be obtained. The box should be made large enough so that the amount of space in the box can easily accommodate the increase it pressure when the cone is operating at high levels. Now in order to reduce the effect of cavity resonance and possible other troubles, the entire inside of the box is lined with s -inch lining of hair wool. This is illustrated in Fig. lE.

Determining Operating Level The proper operating level for an amplifier

working in a large room is a matter of considerable dispute. Some would have the volume very loud, others not quite so loud, while a third group would have the level extremely low depending on the type of program being reproduced. In order to easily compute the proper operating condition, the curve in Fig. 2 was drawn up. Given the constants of a room, it is a fairly easy matter to find the volume in cubic feet, and then by merely locating the value of power corresponding to that volume required, the amplifier power is known.

Now this curve will indicate the level that will be needed to fill the room with sufficient volume so that radiated sound can just be heard all over room. However. as explained before, this level will not be sufficiently high for those people who like to have their programs reproduced at fairly high levels. In other words, it will be necessary to increase the output power of the amplifier if we are to fulfill this item. Gen- erally, a 50% increase in the power output will cover the requirements of any additional gain that may be required.

It follows therefore: Volume in Cubic Feet= 20x30x45- 45.000 Cu.

Ft. Referring to Fig. 2, 45,000 cubic feet corre- spondv to a power level of 5 watts, and in deci- bels this is approximately 29DB.

By increasing our power output by the safety factor of 50% we have: 5-)-2! -_ =7l/g watts or approximately 31 DB.

An examination of the RADto -Caarr tube chart, published in the July issue, will show that two '50 tubes in push -pull will just serve the purpose.

(In a following issue of RADIO-CRAM., the author will discuss the problem of twin speakers. In view of the fact that this topic is of major importance at this time, the Service Man should acquaint himself with full details regarding their use. -Editor,)

DECEMBER, 1932

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PUBLIC ADDRESS ACCESSORIES Include amplifiers front 3000 to 5000 watts, microphones, transformers: stand.. so, kin, attenua:ors, faders, con- trois, cibles, :sal other Items.

Address Dept. CR for booklet on MAYO New and Improved Microphones. Sent F.1E£.

MAYO INSTRUMENT CORPORATION 281 East 137th Se., New York, N. Y.

NEW AND IMPROVED MICROPHONES

$153

371



The adiofa f t Presented on this page are the new

books of the RADIO -CRAFT LI- BRARY -the most complete and au- thentic set of volumes treating indi- vidually, important divisions of radio. Each book has been designed to give radio men the opportunity to specialize in one or more of the popular branches of the industry. The material con-

TO THE RIGHT WILL BE FOUND

A SHORT RESUME OF EACH BOOK

r

ibrary is now complete !

tained in these books will increase your knowledge; you will find them a real help in your work and they will con- tribute to your money earning capacity. Read these books during your spare time at home.

The authors of these books are well - known to everybody. Each one is an expert radio man; an authority on the

Book No. I

RADIO SET ANALYZERS

And How To Use Them

With Full Instructions and De- scriptions of Set Analyzers, Tube Checkers, Oscillators. Etc.

By L. VAN DER MEL

This book explains thoroughly the operation of set analyzers. t checkers. oscillators nd other testing equipment. For every radio man this hook is ex Newly helpful. It rovers every phase of testing and Lives you Valuable short cuts; completely illustrated with photographs and diagrams to facilitate the use of modern testers.

Book No. 2

MODERN VACUUM TUBES

And How They Work

With complete Technical Data on All Standard and Many Special Tubes

By ROBERT HERTZBERG

MODERN VAC t -l'M 'f1' It ES describes the fundamental elec- tron theory which Is the basis of all vacuum tube operation. and goes progressively from the simplest two- element tubes right at to the latest pentodes and thyratrons. It Is written In clear, simple language and Is devoid of the mathematics which is usually so confusing. Valuable reference charts and characteristic curves of standard and special tubes are to lie found. olio diagrams of sockets and pin connections.

Book No. 3

THE SUPERHFTER ODYNE BOOK

All About Superheterodyne&

How They Work. How to Build and How to Service Them

By CLYDE FITCH

'there Is no more fascinating a oteet In the large array of radio

tilts than the famous super - .teralyne circuit. Whether you re a Service Man or experiment-

first -hand knowledge about the ostrortion of superheteralyne re- , ers Is very Important. The .ds on Superheterolynes gives

sly ing principles of their son - sot Ion. right from the very first

made.

Book No. 4

MODERN RADIO HOOK -UPS

The Best Radio Circuits

A Complete Compendium of the Most Important Experimental and Custombuilt Receivers

By R. D. WASHBURNE It Is fascinating to the experi-

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et and to change It into one using a famous hookup that is not found in any mmmfactured set. Many excellent circuits have never been commercialized. but limited only to homeset builders. Thousands of these popular circuits have been requested from time to lime, and in this book we have included over 150 cir-

cuit, which include the famous Peridyne, Cash- A. C.-D.C. Set and others.

Book No. 5

HOW TO BECOME A RADIO SERVICE MAN How to Get Started and How to Make Money in Radio Servicing

By LOUIS MARTIN The ambition of n

e

any n in radio today is to become a first- grade Seriee Sian. It is not as difficult us one might believe. but it cannot he lone In a few short months. Following very earefuiiy the advice of Mr. Martin, who has dealt with the problems of thousands of Service Men. this book deals very carefully with the essential stages In the preparation for qualifying as a Service Man.

Book No. 6

BRINGING ELECTRIC SETS UP TO DATE

With Pentodes. Multi -Mus. Dy- namic Speakers- Complete In- formation How to Modernize A. C., D. C. and Battery Oper- ated Receivers

By CLIFFORD E. DENTON

In thie country there are over ten million electrically operated receivers (hat could Ire utolern- Ized -bv placing

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equipment therm new

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I have circled below the numbers of hooks In the RADIO-CRAFT 'LIBRARY. which you

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372

subject -each is tnoroughly familiar with the field which he represents.

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Bak No. 7

RADIO KINKS AND WRINKLES

For Service Men and Experi menters

A Complete Compendium on the Latest Radio ShortCuts and MoneySavers

By C. W. PALMER If often becomes neceisary for

experimenters and Service Men to 'all upon their memory for some short rut or radio wrinkle that will solve a problem quickly. In business, "short ruts" mean n time and money save, and to the Serv- ice Nan "t hoe saved" means money earned.

This book Is a eompilation of important radio kinks und wrinkles and discusses only such Items as are constantly used today.

Book No. 8

RADIO QUESTIONS AND ANSWERS

A Selection of the Most Impor- tant of 5.000 Questions Submit- ted by Radio Men During the Course of One Year

By R. D. WASHBURNE There have been collected a site

variety of questions which have come into our editorial offices during the past two years, ami only those whose answers would benefit the majority of men engaged in ratio have been Incorporated in this amazing question and answer book. A trememlotuly long list of topics is treated.

Book No. 9

AUTOMOBILE RADIO AND SERVICING

A Complete Treatise on the Sub- ject Covering All Phases from Installing to Servicing and Maintenance

By LOUIS MARTIN

Automobile radios are up and coming. and someone hat to S'rw- lee them properly. It therefore behooves you to read this im- mensely Important new book on the

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A few of the really Interesting chapters: Introduction; .tut t ito Radio I nstal lot ions ; Complete Descriptions of Commercial Auto- motive Receivers; Servicing Auto- motive Receivers; The Ignition System; General Servire Consider- ations; Effects nt Temperature on Power Supply; Conclusion.

Book No. 10

HOME RECORDING AND ALL ABOUT IT

A Complete Treatise on Instan- taneous Recordings, Micro- phones. Recorders. Amplifiers. Commercial Machines, Serv- icing. etc.

By GEORGE J. SALIBA If there is one subject that

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s from the nseritan i 'a I stand point.




AUDIO OSCILLATION (Continued front page 34.1)

CI and C2 were not present, the plate voltage applied to VI would vary as the plate current of V2. Every time the plate current of V2 increased due to a signal, the voltage drop across Rl would increase, decreasing the actual voltage applied to the tube. which decrease would be in phase with the fluctuating plate potential due to the signal.

The result is that the signal is augmented because of the plate current of another tube, and if conditions are correct, the amplifier oscillates or, in some cases, "motorboats." The remedy is to completely isolate the plate circuit so that the A. C. component does not roam outside the bounds of the particular stage. Isola- tion is accomplished by means of resistors or chokes and condensers. Since the same reason- ing holds true for the grid as well as the plate circuit, Fig. 1B representa a completely isolated or tittered stage.

It should be particularly noted that in a push - pull stage of an amplifier, no filtering is necessary, not even a bypass condenser for the grid bias resistor, since the plate currents of the two tubes are 180 degrees out -of- phase, and consequently cancel.

Microphone -to- Speaker Feedback In P. A. systems where the microphone and

speaker are placed in the same room, audio oscillations are bound to result. In this case the oscillations are not due to any fault of the amplifier (provided it does not oscillate with the microphone disconnected), but to the physical location of the loudspeaker with respect to the microphone.

The usual sequence of operation is as follows: The amplifier is turned "on" and the microphone current adjusted. In a little while, or perhaps immediate:y, a beautiful musical howl begins. starting at a low level and increasing in strength

as time goes on. Any attempt to speak into the microphone is useless as the tubes are over- loaded far beyond their capacity -little or no output results. After much cut and trying, the microphone usually finds its way beneath heaps of overcoats, blankets, hats, rags, etc., with the announcer's head buried in close proximity to the microphone. Now, most of the uncertainty can be minimized if the proper precautions are taken regarding the placement of the units.

Oscillation takes place because a small amount of sound coming from the speaker, because of some minute disturbance in the microphone circuit, is fed back into the microphone, amplified. fed back again, etc., in the manner previously described. This may easily be demonstrated by holding the receiver of a home telephone close to its microphone. The only way to atop the oscillation is to prevent the sound from the speaker from reaching the microphone with any appreciable amplitude. Consider the simple sketch of Fig. 2A.

The sound that is directly emitted from the speaker is called the incident sound and, let us say, is radiated from the speaker as shown. If the microphone and amplifier is located in the open air so that the incident sound waves are not reflected by walls. buildings, etc., no oscillation will result.

Suppose, for instance, that the same setup is used but a large vibrant wall (like brick, stone, etc.) is erected in front of the speaker. Part of the incident sound wave will then be reflected by the wall, and if a double -button microphone is used, this reflected sound will enter the microphone and, if strong enough, cause oscillation. This idea is depicted in Fig. 2B. Sound waves act like light waves (acting on a mirror) in that the angle of incidence equals the angle of reflection. Hence, with the arrangement of Fig.


A TRIPLE -TWIN S.W. RECEIVER (Continued from page 357)

Mechanical Construction The physical layout conforms to the ideas

stated. From left to right. Fig. A, there are the R.F. tuner and tube, the detector tuner and tube, the first A.F. stage, the second A.F. stage and the rectifier. The speaker connection socket is mounted on the right rear side; the aerial and ground posts are on the left rear side.

The method of ganging the R.F. and detector coila is extremely simple: two drums are mounted on each shaft. A soft copper band, 'i -inch in width. is so fastened that both shafts rotate in the same directions. A shaft couple is attached to one coil shaft which provides single control for both coils. As both coil forma are identical, there can be no chance of incorrect hookup. The system of ganging is shown in Figs. 2A and 2B.

All high -voltage leads must be heavily insulated to prevent short circuits. Connections should be as short as possible. All negative connections can be made directly to the grounded chassis which is at a negative potential. For best results, it is recommended that the accompanying parts list be thoroughly followed.

List of Parts Two Gen -Win short -wave tuners, wired as shown

in Fig. 2A and 2B, LI. L2; One Hammarlund MC -140 -M dual condenser,

Cl; One Dubilier 1 mf. type PL 800 condenser, C2; One Dubilier 0.5 -mf. type PL 3006 condenser.

C3; One Dubilier .02 -mf. mica condenser, C4; One .015 -mf. mica condenser, C5; One Hammarlund type EC -35 condenser, C6; One Dubilier .001 -mf. mica condenser, C7; One Dubilier 2 mf. type PL 3008 condenser, C8; One Dubilier 25 mf. type PL 4628 condenser, C9; Two Dubilier 8 mf. type PL 3862 condensers,

CIO; One I.R.C. Durham 500-ohm 2 watt Type ME 4

resistor, RI; One I.R.C. Durham 5 -meg. grid leak Type ME 4

resistor, R2: One I.R.C. Durham 3000-ohm 2 watt Type ME 4

resistor, R3;

One I.R.C. Durham 1,500 -ohm 2 watt Type ME 4 resistor. 114;

One I.R.C. Durham 12,500 -ohm 2 watt Type ME 4 resistor, 115 ;

One I.R.C. Durham 250-ohm 2 watt Type ME 4

resistor, 116; One I.R.C. Durham 70-ohm 2 watt Type ME 4

resistor, 117; One I.R.C. Durham 5,000-ohm 2 watt Type ME

4 resistor, R8; One I.A.C. Durham 3,000-ohm 2 watt Type ME 4

resistor, R9; One I.R.C. Durham 3,500-ohm 2 watt Type 4

resistor, 1110; One Centralab 2,000-ohm potentiometer, R11; One Centralab 200.000-ohm potentiometer, R12: One Centralab 20-ohm center -tapped resistor.

R13; One I.R.C. Durham resistor, .1 -meg., R14: Two Sangamo Type AX 3 -to -1 ratio A.F.

transformera, TI. T2; One Kenyon output transformer, pri. impedance

4,000 ohms, T3; One Kenyon power transformer type B245 PT,

T4; One 3 mh. 250 ma. R.F. choke. X; Two Hammarlund R.F. chokes type S.P.C.,

CHI and CH2 ;

One Kenyon 30 by. 125 ma. choke, C113; One dynamic reproducer field coil, CH4; One Kenyon 20 hy., 25 ma. choke. CH5; One Speed type 258 R.F. pentode tube, V1: Two Speed type 256 detector and amplifier tubes,

V2 and V3; One Speed type 295 triple -twin amplifier tube.

V4; One Speed type 280 rectifier tube, VS; Two Blan aluminum coil -shields, length 5% ins..

width 4% ins., height 4116 ins.; One Blan aluminum chassis 21x101,4x3 ins.; Qne Blan aluminum dial -panel 4%x7 ins.: One Blan aluminum switch -panel 2x3 ins.; One Blan aluminum volume- control -panel 2x3

ins.; One National vernier tuning dial, type VND-

400; One off-on switch, SI; One speaker socket, S2: Two drums to fit 14 -in. shaft; One copper belt 18x!4 -in., wire, hardware, etc.


ItPil LLYO

Circular now

ready. Send for

your FREE ropy.

WARD LEONARD MIDGET

REMOTE CONTROL

RELAYS

Working equipment may be hidden in the cellar

or attic. You send and receive from any room. Only sightly units exposed to view.

WARD LEONARD ELECTRIC CO. 41 South Street, Mount Vernon, N. Y.

Please send me a tree copy of your latest bulletin on Midget Remote Control Relays.

Naine

Street

City and State

Call Signal

SHALLCROSS No. 651

%,..) C.4 CY (74 a, ° ss

__ -, e tililh.%L%i

N:.t0 a

RADIO SET TESTER

P.S. 444. sad 7 -peut tubes This new circuit makes It possible for the

service man to construct a light weight and rom - pact up to date radio set tester for all tubes and radio sets In general use. It uses special pet of Shalieross Super Akra -Ohm Wire -Wound Resistors.

Send 6e In stamps for Bulletin 161P containing wiring diagram, construction details. and operating chart.

ORA ,MM WaatUOLY4J»§NkIl.® U"'Q

ELE[TIICaL SPECIALTIES

C'ollingdale, Paa

373



COSMIC QUALITY CONDENSERS Manufactured by one of the greatest condenser organizations. Ac lacted

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CAP. D.C. NET MFD. VOLTS PRICE

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CAP. D.C. NET MFD. VOLTS PRICE

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SEND NO MONEY -Pay the Postman or remit in full and we hand

nd 3e staamp for our 1933 General Catalogue. Distributors and Jobbers write for Pro,.oshlon. FACTORY DISTRIBUTORS

POSTAL RADIO CORP. 137 L1b ,3rty St. New York, N. Y.

QUALITY KENYON

RELIABILITY

KENYON all- purpose amplifier components are the pride of exacting amplifier specialists. KENYON audio, filter and power transformers may be purchased only from auth- orized dealers. Name your favorite jobber and you will receive without any cost detailed schematic diagrams for heavy duty 845 -50 watt, 250, 245, 48 D. C. and 46 class B power amplifiers.

KENYON TRANSFORMER CO., INC. 122 -24 Cypress Ave., New York, N. Y.

AND NOW FLECHTHEIM

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374

REMOTE CONTROL (Continued front pape 363)

Let us observe the cut -off or discontinuance of operations. We press button Nos. 2 and 3. M3 is charged (of no consequence) and the M5 circuit breaker of contact M5 closes. This lead is in series with the circuit breaker on the regenerative unit. which is actuated only by button No. 3. As the two contacts are closed, current flows to relay magnet M2, and the armature disengages clips and the set is dead. To prevent complication of diagrams. the remote control indicators are not shown in the sket h. but are connected in series at point x. As will be noticed, telephone receivers are connected directly across button No. 3, controlling regeneration. This does not impair the operation in the least due to the high resistance of the phones.

"B" battery voltages from a power amplifier are impressed on the phones by use of a high -resistance transformer of the ordinary loudspeaker output type. As previously stated. pressing of button No. 1 actuates M4 and causes the rubber -tired wheel to engage the pulley, while button No. 2 charges 813 and the wheel engages the opposite pulley. This provided the clockwise and counter -clockwise movement of the variable condenser.

There is no limit to the sets of buttons one may use. In the case of the broadcast receivers, a set of buttons and a loudspeaker may be located in every room in the house and controlled at will. (However, there are such things as the man in the room below stealing your particular type of program.)

Suggestions and Summary The layman and constructor may have

around his shop only one set of 16 and 32 pitch worm and worm wheels of very fine pitch, which might suffice.

The slow motion of the tuning condenser is all that is required. As for the driving motor, this should be of the induction type. The writer used an induction fan motor, 110 -volt. A. C., 1.100 R.P.M. A motor with a commutator will cause scratchy noises in the head -phones, unless the builder is adept in the art of choking it with blocking condensers.

One thing to remember is that all housings. bearings, hangers, motor shell, etc., must be grounded. That is, a lead soldered to each, brought together in one common lead. and soldered to the negative or "ground" lead of the receiver. If this is not done, loud noises will prevail in the telephone receivers, when working in the 20- and 40 -meter bands.

For ordinary remote control within the dwelling, the operating voltage of 6 volts D. C. (from a storage battery) will be sufficient: a3 the distance is increased. the voltage should be stepped up. However. if it is con- templated locating the receiver a few miles away, sensitive relays of the "Pony Type" will be required, in addition to the rugged ones operating on 6 volts.

During extensive tests with the author's apparatus. it was found easier to tune stations on short waves than with the human hand on a 100:1 ratio vernier dial on the tuning condenser. With a motor turning 1,100 R.P.M., it takes 21/2 minutes to run from minimum to maximum on the tuning condenser at the vernier ratio, and 48 seconds on the return. If one will turn the rubber tired wheel one rotation with his fingers, it amounts to approximately 1/12,000 part of an inch movement of the rotor plates of the variable condenser. When revolving at a moder- ate speed. and a station flops in, the shaft will continue to rotate about 2 R.P.M. or equivalent to 1/6,000 part of an inch. This is why the station stays "put "; and it is easy to tune from one station to another.

On the other hand, with the remote control unit adapted to the broadcast receiver, this is an ideal method of chasing up and down the scale; knowing that even distant stations may be brought in easily. It is be.' lieved this remote control unit will provide a greater "kick" to the average amateur, than any remote control transmitter he ever saw.

LIST OF PARTS One ratchet wheel (from old alarm clock); Three buzzer or bell magnets (double):


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RADIO -CRAFT for DECEMBER. 193.2



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TEST ADAPTERS (Continued front page 365)

No. 965GG, Fig. 28, tests the 29 and 69 tubes. Models 17 and 19 test only the 29 tube; models AAA1, 40 and 400 series will test both the 29 and 69 with this adapter.

No. 965CG, Fig. 14, is used to test the 41. 42, PA and PZH tubes in the models 40 and AAA1 testers from the '36 socket.

No. 982 is used with the models 17, 19, 40. 40013 and AAA1 testers to test the 82 and 83 tubes. Same as described for Fig. 12.

No. 954KGL tests the first section of a 93 or 95 triple -twin tube. Place in '27 socket of tester; used with the models 17, 19, 40, 400 series and AAA1 testers. Same as described for Fig. 22.

No. 954KG tests the second half of the 93 and 95 tubes. Same as described for Fig. 23.

No. 944PLCR tests the 866 tube in the models 17, 19. 40, 400B and AAA1 testers. In- sert in 2.5 -volt socket. Same as described for Fig. 24.

No. 944BRR is used to test the BR tube in the models 17, 19, 40, 40013. and AAA1 testers. Same as described for Fig. 29.

No. 944BRA is used to test the circuits of the BR tube. Used with the models 90, 99, 99+, 400, 400+, 40013 and AAAI testers. Same as described for Fig. 30.

No. 94413Rß used in connection with the No. 944BRA adapter. Same as described for Fig. 31.

No. 944BRR is used to test the Raytheon BA and BH tubes in the models 17, 19. 40 and 400B testers. May also be used in pairs with the models 99, 99 +, 400A, 400A+, and 400B testers. Same as described for Fig. 32.

No. 955KPT is used with models 40, 400B nd AAAI testers as output -meter adapter for

pentode tubes. Same as described for Fig. 38. No. 955SPT is used with the models 90,

400B, and AAA1 testers for output -meter connection across the plates of a 93 or 95 tube. Same as described for Fig. 34.

No. 966KS is used with the models 19, 40 and AAA1 testers to test the 57 and 58 tubes. Same as described for Fig. 16.

No. 975KP is used to test the 7 -prong tube. Used with the models 17, 19, 40, 400B and AAA1 testers. Same as described for Fig. 85.

No. 950HS is the combination 4- socket adapter; used with the models 17, 19. 40, 400B and AAAI testers. Same as described for Fig. 36.

No. 955DGLC, Fig. 45, Is used with the models 99A and 400A testers for direct reading analysis of the 1st section of triple -twin tube circuits.

No. 964DP, Fig. 64, is used with all models of Supreme analyzers to obtain direct reading analysis of the 2nd section of triple-twin tube circuits.

No. 955GGKC, Fig. 47. enables direct analysis of the Wunderlich 5 -prong tube circuits to be made with all models of Supreme analyzers when it is attached to the UY analyzer plug or its UY adapter and used in conjunction with the No. 955GGKL adapter.

No. 955GGKL, Fig. 48, is placed in the UY analyzer socket when the 6 -prong Wunderlich tube circuits are to be analyzed.

No. 421X, Fig. 37, enables any Supreme plug or its UX adapter to be inserted in a WD11 socket.

No. 968, Fig. 38, enables a WD11 tube to be inserted in the UX socket of any Supreme analyzer.

No. 999, Fig. 39. is used on any Supreme plug or its UX adapter for its insertion into a UV199 socket.

No. 429, Fig. 40, is used in any Supreme analyzer UX socket to take a UV199 tube.

No. 419X, Fig. 42. enables any Supreme plug or its UX adapter to be inserted into a UV type socket.

No. 967, Fig. 43, enables any UV base tube to be placed into any Supreme UX type analyzer socket.

No. 949K, Fig. 4, enables any Supreme analyzer plug to have its filament prongs supplied with filament potential from a receiver using the overhead heater type tubes.

No. 932, Fig. 5, is used with the models 99A and 400A testers for analysis of 22, 32, 34 and 865 tube circuits.

No. 992, Fig. 6, is used with the models (Continued on page 379)

DECEMBER, 1932

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Thus book explains what qualities are needed in such R.F. amplifiers, how they are found in various tube constructions and how they are used in a number of practical radio circuits.

17 RF : How A Vacuum Tube Acts as a Detec- tor: Between the audio and radio frequency amplifier tubes stands the important detector tube. This book covers such subjects as "Mod- ulation and Demodulation," "Detector Operating Points." "Diode Detectors." "How to Calculate Audio Output," "Grid Leak and Condenser Detection," etc.

18 FR: Screen -Grid, Variable Mu and Pentode Tubes: This book covers such subjects as the purpose of the screen -grid tube, screen -grid tube construction and performance, coupling systems used in screen -grid amplifiers, the power pentode and variable mu tubes.

19 FR1: Practical R.F. Circuits and Methods of Controlling Volume: This book sums up and extends the description of radio circuits in previous books, and carries the reader from simple crystal detector circuits to regenerative circuits. It also deals with fixed and tuned R.F. receivers, bypass condensers and R.F. chokes, and cross modulation.

20 FRl: The Radio Frequency Amplifier and flow It Works: An analysis of R.F. amplification is followed in this book by the correction of regeneration, the methods of suppressing oscillation, the elimination of magnetic inter - stage couplings; methods of shielding and R.F. coil problems.

21 FR: The Vacuum Tube as a Generator in Radio Circuits: The important problems of oscillation and modulation in radio circuits receive detailed attention here, with numerous graphs and diagrams. Typical oscillating circuits are presented and explained.

22 FR: Tuners and Wave Filters: This book covers the broad subject of selectivity in radio sets, how it is obtained and what difficulties are encountered. The uses of tuners, wave filters and coupled circuits for good selectivity are thoroughly discussed.

23 Fit: The' Mod, rrt So III rho t rndH, n Re-

BOOK REVIEWS (Continued from page 361)

ceivcr: The theory of the reduction of high frequency radio signals to low frequency, with an analysis of the various parts of a superheterodyne circuit, are presented in this book. Subjects covered are "Oscillators, Mixers and First Detector," "Intermediate Frequency Am- plifiers," "Super- Regeneration." etc.

24 FR: How to Select a Good Receiver: The three tests for a radio receiver, sensitivity, selectivity and fidelity, are analyzed here. The significance of characteristic curves for these qualities is exp:ained and tests are made for a number of standard radio receivers.

25 FR1: Photocells and Clow Lamps: This book describes the principles underlying another modern wonder tube -the photoelectric cell. Its characteristics, the various types, some photocell circuits and the theory and operation of glow lamps are covered.

26 FR: Loudspeakers and How They Oper- ate: The various old and modern loudspeakers, including iron diaphragm units, ba:anced armature units. dynamic units, horn loudspeakers, together with their field of use and their limita- tions. form this book.

27 FR: Loudspeakers, Tone and Output Con- trol Devices: Pursuing the question of loudspeakers. this book describes three quite modern types -the inductor dynamic speaker, the elec- trostatic, and the airplane cloth type. Tube -to- speaker coupling devices, loudspeaker response curves and methods of tone control are also included.

28 FR1: Current Measuring Devices and Their Uses: The operation, methods of construction, and calibration of ammeters, galvano- meters and osci:lographs are described in this book. Thermo -ammeters and thermocouples, magnetic vane electro- dynamometers and the oxide rectifier types are described.

29 FR1: Voltage Measuring Devices and Their Uses: This book describes various types of D.C. and A.C. voltmeters, including methods of high voltage measurements as well as vacuum tube voltage measurements. Sections are also devoted to the measurement of resistance and power.

30 FR: Resistance, Capacity, Inductance and Frequency Measurements: The use of the Wheat- stone bridge, capacity and inductance bridges, measurements of frequency and wavelength and the use of oscillator and resonance meters are covered here.

31 FR: Receiver Refinements: This book goes into the subject of set design, covers the physical construction and requirements for condensers and outlines the requirements of a radio receiver that has simplicity of operation as well as positive control.

32 FRl: Short Wave Receivers and Trans- mitters: The new and growing field of short wave reception and transmission forms the basis of this book. The advantages of short wave apparatus. the detector circuit, short wave condensers and coils, the audio amplifier, the R.F. system, shielding the short wave receiver. and a number of short wave circuits for the designer are presented. Adjustment and operation of short wave receivers are also covered.

33 FR1: Transmitting Antennas and Their Radiation Characteristics: The antenna is the link between the transmitter and the receiver. The theory of antenna design, an analysis of ground and counterpoise systems, a description of antenna constants and antenna couplings. as well as the interesting operation of beam antennas, are among the subjects presented.

34 FR: Design of Power Audio Amplifiers: This book covers the problems that arise in the design and operation of various types of power amplifiers, covering both theory and practice. The methods of calculating the amount of amplification necessary to supp:y a definite amount of power for various loads are fully explained.

35 FR: A Typical Broadcast Station: This book takes the reader through each division of a modern broadcast studio. emphasizing the importance and particular role of each. It covers the studio, the monitoring control room, the master control room, the auxiliary equipment. etc., from the microphone into which the speaker talks to the antenna from which waves are radiated.

THOUSANDS OF RADIO MEN Have asked for a book of this kind during the past year

the RADIO -CRAFT INDEX It contains a thorough, alphabetical and topical arrangement of every article and subject which has been published in all the issues of RADIO -CRAFT from July, 1929 to June, 1932

RADIO Men have conclusively proved to us the need and practicability for a book which has included in it. a comprehensive and complete listing of every

article which has thus far been published in RADIO -CRAFT. A book which has each topic so sub- divided and cross -indexed that a mere a glance at a subject will give you any number of classifications and uses of it. For example, if you

look at tubes, you find under this topic. various sub -titles, general. power, trans-

mitting, photo -cells, testing of tubes, thyratrons. etc. Every article or notice in the book has been considered so deeply important that when you refer to

a certain classification, hated below the ma in topic, you will find perhaps dozen or more articles treating the subject from different angles. The author Mail coupon below for your copy of the RADIO -CRAFT I. DE X.

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rately compiled, by C. W. Palmer, one of radio's foremost writers. that in less than two minutes you can n turn to any article -needless to wade through all the issues of RADIO- CRAFT which have been published during the past three years. The RADIO- CRAFT INDEX is exactly the sanie size as the monthly magazine. It can be conveniently kept on file c ith the copies of the magazine -ready for w, e

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ANTENNA SYSTEMS- CABINETS- CIRCUITS-

t',,,,, ,t, err ial Experimental

CODE - COILS AND TUNING - COMPONENTS - COOPERATIVE LABORATORY - DETECTORS AND RECTIFIERS- EDUCATION- INTERFERENCE AND HUM

ELIMINATION - KINKS- MANUFACTURING - METERS AND TESTING EQUIP -

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AND PROJECTION- MUSICAL INSTRUMENTS - NEUTRALIZING- NOVELTIES-

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REMOTE CONTROL - SELLING AND MONEY MAKING SERVICING-

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ltroadrast Short -Ware

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REPRDDUC.

TOOLS - TRANSFORMERS-

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TRANSMISSION - Generd

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TUBES - General Pentole Photo -Cells Test lite Thyratron

LIST OF BROADCAST. SHORT- WAVE AND TELEVISION STA- TIONS-

ABSOLUTELY NOTHING WHICH HAS APPEARED IN RADIO -CRAFT BEEN OMITTED FROM THIS VALUABLE. COMPILATION

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HAS

DECEMBER, 1932

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96 PAGES OF NEW DATA HAVE BEEN

ADDED TO THE

OFFICIAL REFRIGERATION SERVICE MANUAL

r

To bring this useful service manual right up-to -date. Mr. L. K. Wright. the editor of the OFFICIAL RE- FRIGERATION SERV- ICE MANUAL. has added wealth of material on new electric refrigerators, and older models as well. As usual every refrigerator has been accurately described froto the view- point of servicing - diagrams to Illustrate the essential parts, so simplified that repairs can easily be made. The addition of these

w pages will not In- crease the cost of the hook to those who order their copy wow.

Here Are Some Of The Important Chapter:

I :.Iraluct Ion to the Re- f ri great Ion Servicing Ilusineas

Ili story of Refrigeration I ondamentals of

Refrigeration Il,cription of All

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Std'ra outdo Shooting

I it Parts, Valves and .t utomatio }Equipment

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nufacturers of I :tbinets

I bdrigerants and Auto- mat it EquIPlnent and Ni any 'filter limn) -

tant Chapters

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RADIO ENCYCLOPEDIA 1st Edition

WD HAVfl on Lanf Jro t 111)1'NI) conies of this valuable ba,k. and we are dis- - Dosing of them at a price i,hl,h Iles not eon corer the cost of THE BOOK the paper and Printing. The books are in first -class condition, sewed and stitched but unbound. You can put a cover on yourself ur your bookbinder can do It at a very small expense.

This Indispensable radio reference book contains over 1.930 definitions. 549 photo repro- ductions. drawingo, nd diagrams. The sire of the book Is 9 by 12 inches. It tonic ins 16s pages. is

Practically every definition kipaper he

book is illustrated, and all the subjects are arranged in alphabetical order with numerous broies and charts distributed throughout the text.

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SHORT CUTS ( Continued irone. )luge .152)

A PLATE CIRCUIT ADAPTER Jack S. Stanton

THE adapter illustrated in Fig. 3, when placed In a rectifier socket and the rectifier placed

in the adapter, will enable the Service Man to work on a radio receiver power pack without getting a shock. Also, this adapter is a time saver since it permits pre -heating tubes, while the "B" supply circuit is opened by means of switch SW. Furthermore. this adapter may be used to tap the high voltage D.C. from the rectifier tube in the set, thereby providing an external "B" supply for demonstrating, for instance, a short-wave converter.

In the latter instance, a filter choke. condenser and voltage divider complete the "B" supply for the converter; two of the six wires in the adapter carry 6 volts for the rectifier filament and this potential may be used to operate a trouble light or as a positive lead of the high voltage D.C. for the converter while an additional wire. connected to the chassis of the set or the ground. provides a negative, high -voltage connection.

For the cable, the writer braided six 18 in. lengths of flexible. rubber -covered hookup wire. Strict care must be taken to maintain the high insulation necessary in devices operating at these high potential circuits.

A MULTIPLE CONTACT AND ANA- LYZER SWITCH

J. L. Henderson

NECESSITY, the mother of invention, ac- counts for the switch illustrated in Fig. 4.

It was built in lieu of the three -gang six -pole switch called for in the article, "The RADIO- CRAFT Universal Analyzer," which appeared in the September, 1932 issue of RADIO- CRAFT.

The arrangement illustrated in Fig. 4 was built from a "junk box" and therefore does not carry dimensions. Needless to say, the arrangement comprises a few scraps of bakelite, two jack bridges and nuts, a heavy spring, a piece of %a -in. shaft, some spring copper, and 18 switch contact points. plus miscellaneous set screws and machine screws.

Tap the contact points into the bakelite to make a more solid job. Place the contacts close together in order to prevent the circuits being opened, thus damaging the meter movements during a change of position under load ; finally, surface off the contacts with fine sandpaper glued to a board. The indicator knob is slotted to show one number at a time.

KINKS (Continued front page 354)

HOW TO MAKE A TUNING FORK OSCILLATOR C. W. Molette

MANY technicians would like to measure the response of loudspeakers and A.F. ampli-

fiers, but lack the necessary cash to build a reliable A.F. oscillator. Therefore, a description of an oscillator built by the writer along the lines of Fig. 4 may be of general interest. Since every tuning fork has a natural period of its own, a fork will be required for each test frequency; a complete set is not expensive. However. one fork may be adjusted to one of several frequencies, by means of sliding weights on the prong as shown at X in Fig. 4A. Forks may be purchased with accurate marks to show where to set the weights for different frequencies. The fork is set into vibration by tapping the key button. Fig. 4A.

Coil L is wound with No. 36 to 40 enam. wire on an iron -core form which will just fit inside of the individual tuning fork; of course, the ends of the core must clear the tines of the fork. The wire from a magnetic reproducer will be about right as to size and quantity.

The output of this inductance feeds into an A.F. amplifier; the connections for this unit are shown in Fig. 4B.

In Fig. 4C are shown the connections of a modulator. If this unit is used. its input connects to the output of the amplifier of Fig. 4B. The output of the modulator may be con -

(Continued en page 379)

DECEMBER, 1932

Get Into a Line Where There's Action - Every Day -And a Payday Every Week -You be the Boss! Right now while hundreds are looking for work m here there isn't any. the radio service field can use trained men. With the proper training and the necessary equipment, you can enter this field and make a comfortable living. We include with our course this modern set analyzer and trouble shooter without any extra charge. This piece of equipment has proved to be a valuable help to our members. After brief period o training. you can take the set analyzer out on se v ee calls and really compete with "old timers." W show you how to wire rooms for radio- Install auto sets -build and Install short -wave receivers -anal ze and repair all types of radio sets -and many o her profitable jobs can be yours. Teaching you this Interesting w rk Is our business and we have provided ourselves with every Iariflty to help you learn quickly yet thoroughly. If you possess average intelligence and he desire to make real progress on your own merits. you will be interested.

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377

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Man. If you want diagrams of commercial radio receivers, we are now prepared to give you

RUSH SERVICE In the three OFFICIAL RADIO SERVICE

MANUALS published by us so far. we are listing almost 5,000 diagrams of commercial radio sets manufactured in America.

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We have, however, had an increasing demand of late from Radio Service Men who are not necessarily owners of any of the MANUALS but who wish to get one or more diagrams. We are now prepared to send you such diagrams on a rush order plan. We realize that if you ,want one of these diagrams you want it qMich.

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OSCILLATION (Continued from page 373)

2B only a small amount of energy is fed back, which may be below the level required for oscillation to take place.

In the diagram of Fig. 3 which illustrates conditions in which the microphone and speaker are located in the same room, the microphone is shown as a black dot in order to simulate actual conditions.

A sound wave issuing from the speaker is reflected by the walls surrounding the speaker and ultimately finds it way back to the microphone; oscillation, therefore, results. Suppose, for example, it is not possible to change the location of either the microphone or speaker, but the oscillation must be eliminated, then what? BATTERY- OPERATED

From the above considerations, we know that P.A. SYSTEM it is the energy in the reflected sound wave that

ultimately reaches the microphone, causing oscillation. And since the positions of either ( Continued from page 364) the microphone or speaker cannot change (by watt, (12) :

hypotheses) the only resort we have is to reduce One Acratest carbon resistor, 500,000 ohms, 1

the energy in the reflected waves. watt, (14) When a sound wave strikes a surface, it is One Yaxley wire wound resistor, 2 ohms, (28)

either absorbed, or reflected. (Practically, of One Acratest cartridge type condenser, .03 -mf., course, a little of either always happens, but in 300 volts, (13) most cases, more of one than another.) If the Three five -prong wafer sockets, (15), (17), sound wave is absorbed, then the reflected wave (18): (it any) will be very weak ; reverberation will One Acratest input class B transformer, No. he absent ; and, the room will be "dead." If 7127, (16): the sound wave is reflected, then the conditions One Acratest output transformer, No. 7129, described above will obtain -feedback, oscillation, (19) :

etc. For this reason, it is well to line the walls One Acratest output terminal strip No. 7149, of the room in which the microphone and ampli- (20), (21), (22), (23), (24), (25) :

fiat are to be used with curtains, drapes, carpets, One Flechtheim filter condenser, 4 mf., 200 volts, etc., or anything that will absorb sound -not D.C. type GB -400, (26) ;

reflect it to a great extent. In this manner, One Korrol chassis to specification: the energy in the reflected waves is reduced to a One Best magnetic speaker, 4,000 -ohm im- value which is just insufficient to cause oscil- pedance; lation. One wooden carrying case;

It would be useless. of course, to place sound One ER type '32 tube: rbsorbing material on that part of the wall One ER type '33 tube; ..here the incident or reflected waves do not Two ER type 49 tubes: touch. The idea, then. is to trace the angle of Three ER 45 -volt "B" batteries; the sound wave from the speaker and place the Two Eveready dry cells; material on that portion of the wall where the One Eveready "C" battery, with 16.5 -volt tap.

sound would strike. Pictured in this article is a sample of sound absorbing material manufactured by Ames, Aceves and King which resembles corrugated board and which has a high and uniform coefficient of absorption (ability to absorb sound).

It also sometimes happens that the microphone and the speaker may not be in the same room and yet audio oscillation results. The feedback, in this case, results from the transmission sit the sound through the wall connecting the two rooms. The obvious remedy then, is to "treat" the wall causing the trouble. It is not a simple job for the layman to handle. Considerable patience and experience is sometimes required which will be well rewarded -if done properly.

378 RADIO -C

P.A. AMPLIFIERS (Continued from page 353)

loudspeakers in the individual class rooms. If the school auditorium is also the town

meeting place and the center of political and social activities, you have even a stronger argument. Always emphasize the fact that speakers, entertainers. etc., do not have to exert themselves in order to fill the hall; they merely speak or sing in their natural voices and the P.A. unit does the rest. Play up the microphone stuff. The "mike" has a magic, irre- sistible attraction that rarely fails to "get" people who step in front of it.

You may wonder why factories are included on the list of prospects. The answer is that they represent a veritable gold mine. While many plants are running at reduced capacity, there are plenty that are still busy, and there never has been any let up in some lines. For creating and maintaining employee morale, particularly in factories where the work is monoto- nous, there is nothing like a P.A. system reproducing phonograph music through a few scattered loudspeakers. Numerous companies are using this scheme and are finding it highly effective, especially if the workers are women and girls.

The practice varies. Some factory managers keep the music running almost continually, at low volume, if the nature of the work does not require very great concentration. Others turn on a record every hour or so, and keep the system alive all during the lunch hour. The usual result is a factory full of smiling, singing people, who are likely to forget some of their troubles and do better work. An incidental value of such a P.A. system is for summoning executives to the telephone and for making announcements in general.

As in other fields of salesmanship, nothing is as effective as a demonstration. In the case of P.A. amplifiers you can "make them talk for themselves." People who have had no experience with such devices do not fully appreciate their possibilities, and they must be made to talk into a mike and hear some real phonograph music. This means you must have an amplifier available and must be prepared to demonstrate it on the prospects' own ground or in some other easily accessible place. You must not expect a man to buy something "sight unseen," or rather "sound unheard," in this case. Your purchase of one amplifier to start with represents your investment in a business. Once you have installed the first job you can then bring prospects around to hear it under actual working conditions, and things will be easier from then on.

Make sure the local papers know about that first installation. They are always anxious to get local news and may be able to give you extremely valuable publicity. Don't be modest; call 'em up and tell them all about it. If you don't blow your own horn no one else will.

As an example of the many excellent amplifiers that Service Men can obtain, the new Lafayette class "B" 28 -watt job is representative. It makes use of one of the new type 67 tubes, three type 46 and one type 83 mercury vapor rectifier, in the unusual circuit shown. The input, from microphone, phonograph or radio, is lead to the grid side of the 57. This tube is directly coupled to a 46 by the well known Loftin -White method, the 46 in turn feeding two more 46's in a push -pull output stage. The output of this compact outfit, which measures only 111 by 20 by 8 inches, is sufficient to drive TWENTY full size dynamio speakers.

The schematic diagram and the accompanying illustration will give the Service Man a complete technical story on this versatile amplifier. To accommodate various combinations of speakers and lengths of lines, the secondary of the output transformer is tapped in two sections to give output impedances of 4, 8, 15, 500 and 2.000 ohms.

In forthcoming articles the writer will discuss permanent outdoor installations. mobile, portable and temporary installations, inter- office systems and incidental technical problems such as line matching, acoustic feed back, use and care of accessories, etc. If any Service Man is confronted with an immediate problem in any of these classifications the writer will be glad to correspond with him and offer all possible assistance.

RAFT for DECEMBER, 1932



NEW TUBES (Continued from page 367)

The following details obtain for the 59: Heater voltage, 2.5; heater current, 2 amp. In the following data the first numeral refers to a class A triode, the second to the pentode connection, and the third to the class B connection: Plate voltage, 250, 250. 400; control -grid voltage. -28. -18. 0; screen -grid voltage -, 250 volts. -; plate current, 30 ma.. 35 ma., 15 ma. (no signal); amplification factor, 6, 6, 6; load impedance, 5,000 ohms, 7,000 ohms, 1.500 ohms; output. 1.25 watts, 2.6 watts, 20 watts (maximum for two tubes).

A curve showing the relative distortions present for three different connections is shown in Fig. 7.

TUNING CONTROL (Continued from page J74)

Four buzzer or bell magnets (single) ;

One induction motor: Four adjustable hangers, with bearings ({¡

hole) ;

Eight inches of f, in. steel shaft: Three collars, is in. hole; One grooved pulley, 1 in. or more, y}, in.

hole; One grooved pulley, 3á in. or more, is in.

hole; Two flat faced pulleys, 1Si: in.. r} in. bole

(diameter of pulley- optional) :

One worm gear, 16 pitch, ya in. hole; One worm wheel, 16 pitch, Vs in. hole; One worm gear, 32 pitch. % in. hole; One worm wheel. 32 pitch, ya in. hole; One length ya in. diameter steel shaft: One reducing gear. 10 to 1 ratio (spur gears); One sprocket gear. 1 inch, ass -in. hole; One sprocket gear, % in. (to fit motor shaft); One length (12 inches approximate) chain.

ADAPTERS ( Continued from page 375)

99A and 400A testers for analysis of '24, '35, '36, '38, '39, 44 and '51 tube circuits.

No. 974, Fig. 7, is used with models 99A, 99A +, 400A, 400A+ and 400E for analysis of 33, 46. 47, GA, LA and PZ circuits.

No. 956SS, Fig. 81, is used with the model AAA1 tester being attached to the analyzer plug and No. 965SL is used to hold a 6 -prong tube in the 5 -prong analyzer socket for circuit tests of 29. 41, 42, 65, 57, 58, 69, 86, 89, PA. PZH and Wunderlich tubes.

No. 946SS1H, Fig. 82, is used with the model. 90 series. 1J, and 2J and also model 400B -N4 testers series for attachment to the analyzer plug. Used in conjunction with the No. 965SL adapter which is used in the 6- prong analyzer socket while making circuit analysis of 29, 41, 42, 55, 67. 58, 69, 85, 89, PA, PZH and Wunderlich tubes.

No. 946SS Fig. 83, is used with the model 90, aeries 3J, 4J, and 5.1 testers for attachment to the analyzer plug. Used with the No. 966SL adapter which is placed in the 5 -prong analyzer socket for analyzing the circuits of 29. 41, 42, 65, 57, 68, 69, 85, 87, PA, PZH and Wunderlich tubes.

KINKS (Continued from page 377)

netted in series with the plate -circuit power supply to an R.F. service oscillator.

Qualitative tests may be made by ear; quan- titative values may be obtained by connecting a V.T. voltmeter across the output of the AI'. amplifier.

Be sure that the low -ratio A.F. transformers. TI and T2, are of high- efficiency type.

"MIKE AND IKE -" There are thirty million radios in

the United States. Mike country, may she never be wrong! Mike country, may she always be right! But right or wrong Mike country! -H. L Phillips (N. Y. Sun).

A STATEMENT By Hugo Gernsback

IHAVE been publishing radio magazines since 1905, and during this period I have learned let know what radio readers want.

Last summer I made a trip through central Europe, in order to acquaint myself with radio conditions as they are In Europe today. I was sinned at the tremendous amount of radio experimenting that is now going on. In practically all of the western European countries. I found conditions similar to those during the 1921 -1923 boom in America. Radio stores were prospering and doing a land -office business. The reason. of ( ourse. is the intense Interest of the European radio experimenters who are building sets on scale undreamt of before.

The European radio publications are abounding with new circuits and new radio developments that have found their way slowly over to the United States. The reason Is that. since there is such a tremendous amount of original radio engineering going on in this country, there has been no publication that catered to the foreign developments. All the American radio publications must, of necessity, retort the American activities first and, as a rule. have no room toit for what is going on in Europe unless an epoch- making development appears.

I therefore conceived the idea of bringing to my American readers a totally different radio publication. the like of which has never been published before; and the result is RADIO REVIEW ANI) TELEVISION NEWS.

is not entirety a new magazine; It is. really. two magazines in one. A section devoted to television has been retained. which will report in every Issue, the major American and European television advances; but the big. ,Pont section is given over to an international radio digest. This magazine, therefore, perform the function that, for instance. the LiTEII ARY DIGEST is

s serving in literature. You may not be aware of the

fact that there are some loo radio publications na printed outside of the United State,; but from all of these publications RADIO 1t 5YJEW Is extracting the best -the Neil Meat--which you want.

There are literally t material

of n circuits, due to the new tubes, and there is so much new material for the exnerlmenter that I would have to till several pages to tell you all about it.

RADIO REVIEW AND TELEVISION NEWS then It a new mirror, which will accurately show you a true perspective of what is going on In radio all over the world, and will give you material in such profusion as you never have seen before. Hundreds of new radio hook -ups. special

new money-making kinks, new ney- making Ideas galore. You will find here the latest radio eircuitvand sets from France. Germany. England, Italy, Russia, Norway and even Japan.

Dozens of translators have been busy to make the first issue of the new combination maggazine a memorable one, that you will not soon forget, and you will s mier why I hadn't done it before.

And now I frill ask you for s favor. Go to the nearest newsstand and get a cosy of RADIO RE VIEW AND TELEVISION NEWS. Pay your quarter for it, es home and look it over. If at the end of a week, you And that for any reason you do not like the magazine, return it to me with a letter staling why you don't rant It and I will refund your liar ter, so sure am I that you will not with to be with out this magazine in the fu turo.

It o you isn't have to pay for r the magazine an- less you think it is what you are looking for.

If your newsdealer is sold out or does not stock the mag- azlneoend 2 r. to us (seeeou- on); money refunded if you

don't want the magazine. I thank you in advance for

your patience and for your confidence.

Cordially )'font

YOU NEED NOT PAY FOR THIS MAGAZINE IF YOU DON'T LIKE IT. YOU ARE THE SOLE JUDGE

IMPORTANT Do not confuse the former TELEVISION NEWS with this magazine. RADIO REVIEW AND TELEVISION NEWS are two distinct magazines in one.

A few of the outstanding articles in the RADIO REVIEW section: NEW: Play Music on Your Radio

Set: Build the sensational THERE - MIN ADAPTER

1 Tube D.C. Power -Loudspeaker Special

The VM -Three Receiver Tho Diodion Screen -Grid Circuit Improved Reinertz Hook -Up Preventing Radiation from the Local

Oscillator New Transmitting Antenna Decreases

"Skip Zone" The Champion Three -a Prize french

Receiver Adding Automatic 'Volume Control A D.C. Super- lleterotlyne Locating Hidden idden l'lpes by Radio One Tube Super -Regenerative Loop

Receiver A Two for 7 Meters Review of American Radio Literature Digest of American and Foreign

filante Dozen, of Circuits. Kinks and Prac-

tical Suggestions

Features in TELEVISION NEWS section:

.t Combination Sicht and Sound Ito -civet.

A 5 -Meter Super -Regenerative Television 'itoceiver New Baird Televisor Built Like Camera Television Transmitter for Topical Events Diode Detection for Television Receivers Myers Mercury Vapor Television lamp Schedule of Active Television Stations Television Question hoc


RADIO REVIEW AND TELEVISION NEWS 'J5 l'ark Place RC -12 -32 New York Pity (Mark X in Square Which Offer You Desire) Gentlemen:

As per your special offer. I enclose $1.25 (Canada and Foreign $1.501 for which enter my subscription to RADIO REVIEW AND TELEVISION NEWS for one year

Send me the current Issue of RADIO REVIEW AND TELEVISION NEWS, for which I enclose 25c (1. S. stamps or coin accepted) with the full understanding that if I do not like the magazine you will refund the money as explained above

Name

Address

t'I,y and State

379



READERS' BUREAU On this page are listed manufacturers' catalogs and booklets, chosen because they are of interest to readers of RADIO - CRAFT. You can obtain copies FREE by using the coupon below.

6. CLAROSTAT CONTROL HANDBOOK. A large 32 -page book containing detailed specifications of volume controls, attenuators, constant -impedance controls, phonograph pickup faders, tone controls, line ballasts, rheostats, potentiometers and fixed resistors of various kinds, together with valuable circuit -design data. Contains many diagrams and charts, and a guide of replacement volume and tone controls for many commercial receivers. Clarostat Manufacturing Com- pany, Inc.

7. SPEED RADIO TUBES. Contains a chart of the electrical characteristics of the Speed tubes, and also a convenient list of broadcasting stations with space for dial settings. Cable Radio Tube Corporation.

8. ELIrTRAn PRODUCTS. Descriptions of the full line of Electrad volume controls, voltage dividers, vitreous resistors, Truvolt adjustable resistors, amplifiers and other devices for radio and electrical applications. Among other diagrams, it includes twenty -four circuits showing the placement of volume controls in different types of broadcast receivers. Electrad, Inc.

9. RECTIFIER TYPE INSTRUMENTS. This type of instrument is used principally for measuring alternating currents of such small magnitude that they cannot be measured readily with ordinary types of A.C. instruments. It consists of a sensitive D.C. meter used in conjunction with a rectifier made of four sets of copper -oxide disks arranged in the four arms of a Wheat- stone bridge circuit. This folder, written by the chief engineer of the Weston company, describes the principles of operation, and is very interesting and instructive. Weston Electrical Instru- ment Corporation.

11. SUPREME INSTRUMENTS. Contains lengthy descriptions of the Supreme service instruments, including the AAA1 Diagnometer, which is five instruments in one, the model 90 analyzer, the model 40 tube tester and the models 60 and 70 oscillators. Interesting to the Service Man because it tells how his work is facilitated by ingeniously -designed test equipment that indicates the condition of an entire set in a few minutes. New test apparatus to take care of the new tubes is also described. Supreme In- strument Corporation.

19. A BAPTISM OF FIRE. Centralab fixed resistors are made by forcing a carefully calibrated resistance material through a plastic ceramic material, and then baking both under terrific heat. This booklet describes the manufacturing process in detail, and lists the advantages claimed for fixed resistors of this type. It is interestingly written and illustrated, and makes good reading. Central Radio Laboratories, Inc.

21. READRITE RADIO INSTRUMENTS. This sixteen -page pamphlet contains some valuable hints on the testing of electrolytic condensers, as well as descriptions of the full line of popular -priced Readrite instruments. Worth having. Readrite Meter Works.

26. AEROVOX 1932 CONDENSER AND RESISTOR MANUAL AND CATALOG. This 48 -page booklet is worth having and saving. In addition to very complete specifications on the full line of Aero- vox paper, mica and electrolytic condensers, and vitreous enamel, carbon and wire -bound resistors, it contains a great deal of information and data on condensers and resistors in general which the Service Man and experimenter will be able to apply to his everyday problems. Aerovox Wireless Corporation.

27. DUBILIIIR CONDENSERS. The name Dubilier being synonomous with condensers in the minds of many people. the latest catalog of Dubilier condensers is sure to be of interest to all classes of radio users. This 16 -page booklet describes the entire line of receiving condensers and tells something of the historical background of the company. The special service kit and replacement units are recommended to the attention of Service Men. Included with the catalog is an instructive technical article dealing with electrolytic condensers. Dubilier Condenser Corpora- tion.

28. HAMMARLUND PRECISION PRODUCTS. Midget variable condensers and their numerous applications in short -wave and broadcast receivers are discussed in a folder accompanying the complete catalog. of Hammarlund variable condensers and coils. Some excellent circuit kinks are given. The catalog contains dimensional drawings of the popular Hammarlund midgets which may be of assistance to constructors designing small re-

ceivers. Hammarlund Manufacturing Company, Inc.

65. PUILCO PARTS CATALOG. This new catalog will undoubtedly be of great help to all radio Service Men because it contains the only official, complete list of the more common replacement parts used in every Philco receiver from the very beginning of the company to the present time. The manufacturers are anxious to co- operate with Service Men and offer this catalog to all who want it. Philco Radio & Television Corp.

59. PRACTICAL RADIO ENGINEERING. This handsomely prepared 24 -page brochure describes in great detail the home -study courses in radio engineering offered by the school mentioned below. These are intended for the more advanced type of student who is interested in actual radio engineering, as they include mathematics running up to vector analysis, use of the slide rule, and even the operation of 60- kilowatt broadcasting stations. The instruction is intended to bridge the gap between college study which emphasizes the theoretical side and the "practical" courses which end with service work. The serious radio man who is looking ahead will find this booklet worth reading. Capitol Radio Engineering In- stitute.

63. TtlE AKAFORMER. The Akaformer, described in this folder, is a coupling device that hooks right on to the aerial wire, and connects to the set through a shielded down lead. The combination tends to reduce noise in the set picked up by the usual lead in, which, running along the side of the building, is more readily affected by elevator motors, vacuum cleaners. dentists' drills and other electrical machinery than the flat top section of the serial proper. The device is inexpensive and is easily installed, and is thereby a very profitable item for Service Men located in districts where artificial noise is very troublesome. Amy, Aceves & King, Inc.

64. SYLVANIA RADIO TUBES. So many new tubes have appeared during the past several months that tube charts printed as recently as the Spring are incomplete and therefore of little value for reference purposes. Readers desiring new and complete charts for their shop wall will find the new Sylvania chart very desirable. It measures 11 by 17 inches when unfolded and shows bottom views of the tube bases in addition to full average characteristics of old tubes dating back to the 199 and 200A and all the new tubes including the latest 6.3 and 2.6 volt types. Special mention is made of the 56, 67, 58, 46, and 82 tubes ; complete data are also given on the 38, 41, 69, 42 and 44. Hygrade Sylvania Corporation.

66. WHOLESALE RADIO SERVICE CATALOG. The 1932 Spring and Summer Radio Catalog of the Wholesale Radio Service Company is the kind of catalog the radio Service Man and experimenter will carry around with him all the time in his back pocket. Measuring 7 by 10t/ß inches and containing 100 pages, it is one of the most complete catalogs we have ever seen. It includes everything from soldering lugs to all -wave combinations, and is of particular value to the Serv- ice Man because of its handy lists of replacement parts for standard receivers. Wholesale Radio Service Company, Inc.

'17. SAMSON MICROPHONES AND ACCESSORIES. The well -known line of Samson "PAM" amplifiers is now being supplemented by a series of high quality microphones and accessories, which are described in a bulletin which gives their technical characteristics. The first seven "mikes" are of the double- carbon- button type. Four of these are intended for suspension in the familiar ring stand, two are of the band type, and the last resembles an ordinary desk telephone. The second group comprises three dynamic microphones, which use the same unit in different forms of mounting. The third and last group is a pair of condenser "mikes" designed for broadcasting purposes. All these microphones are of interest to public address and broadcasting specialists. Samson Electric Company.

80. FLECHTHEIM CONDENSERS. A wide variety of fixed condensers, ranging from tiny midget, the size of postage stamps, to heavy transmitting units a foot high, are described and illustrated in the latest Flechtheim catalog. This is very useful for reference in design and service work. as it gives the mechanical dimensions and electrical characteristics of all models in minute detail. A. M. Flechtheim & Co.

81. I. R. C. RESISTOR CATALOG. This sixteen - page catalog describes a very complete line of fixed resistors for radio purposes. It include,

full performance characteristics, so that a Serv- ice Man or an experimenter with a particular requirement in mind can select exactly the right unit for his purpose. A section in the back contains valuable data on the conversion of milliameters into ohmmeters and voltmeters, and on the extension of voltmeter and ammeter rangea. This catalog is well worth saving. International Resistance Company.

82. MILES BULLETINS. Bulletin J features midget and lapel microphones, home broadcast units and portable group -address amplifiers. The use of a lapel "mike' for faking in announcements on the family radio receiver is suggested as a home entertainment stunt. Bulletin M deals with simple private communication systems, for which there are big possibilities in offices, factories, homes etc. Miles Reproducer Co.

84. POSTAI. TUBE CHART. Service Men and others who have been confused by the recent avalanche of new tubes will welcome this large chart, which shows the pin arrangement and socket connections of the latest types. It is very handy for reference purposes in the shop or out in the field. Postal Radio Corp.

85. CONTINENTAL SUPPRESSORS.. This special bulletin describes suppressor resistors and condensers for automobile ignition systems. Some valuable suggestions for installing the devices and for eliminating interference are given. The method of using suppressors on a typical ignition system is illustrated. Continental Carbon Inc.

86. YAXLEY AND ELKON CATALOGS. The Yax- ley catalog is valuable for the Service Man because it lists numerous rheostats, potentiometers, volume controls, replacement controls and resist, ances for service work. Detailed dimension drawings are included; this feature will be appreci- ated by every Service Man who has been called on to install replacement units in cramped receivers. Two pages of volume control replacement information are included. along with four- teen diagrams showing different circuit positions for such controls.

The Elkon catalog is devoted exclusively to dry electrolytic high voltage condensers for filter and bypass purposes. It too includes valuable replacement data on commercial receivers. P. R. Mallory & Co.

87. OHMITE RESISTORS. Hundreds of fixed resistors of different values and power rating are listed in this six -page bulletin. The following types are included: vitreous enameled fixed and semi- variable, meter multipliers, power rheostats, transmitting grid leaks and power pack units. A useful addition to every Service Man's and experimenters file. Ohruite Manu- facturing Company.

88. PRECISION TYPE HIGH RESISTANCE UNITS. This bulletin is devoted to special resistance units designed for applications where precision of value is an important consideration. Fbr instance: television amplifiers, voltmeter multiplers. ammeter shunts, photo -cell circuits. sound head amplifiers. attenuators, decade boxes and resistance bridges. The tolerance of the units described is 1% plus or minus of the rated values. Resistors ranging from .26 ohm to 6 megohms are listed. Precision Resistor Co.

RADIO -CRAFT 5 -88 Readers Bureau 96 -98 Park Place, New York. N. Y.

Please send me free of charge the following booklets indicated by numbers in the published list above: No.

Name Address City State

(Pleat* check the following) I am

(1) Service Man (2) Experimenter (3) Dea:er (4) Jobber

(5) Radio Engineer (6) Licensed Amateur

(7) Professional or Amateur Set Builder

This coupon will not be honored unless you check off your classification above.

380 RADIO -CRAFT fir DECEMBER, 1932



Hundreds of these Short Wave Sets are sold each week! POWERTONE BATTERY -OPERATED -15 TO 200 METERS SHORT WAVE RECEIVERS

GOING FAST YES, stronger than ever. so do we voice our and

countless other opinions on this remarkable shortwave battery operated receiver. Faster than ever in sales volume, for the public has caught up with us in voicing their enthusiasm on results with this receiver. Never before has reception such as this been available on any two or three tube battery operated shortwave set.

The use of the new two volt, air cell, tubes increase reception sensitivity, and selectivity, furthermore current consumption is kept at a minimum. Provisions are made within the receiver to reduce three volts to two so that dry cells can be utilized.

The set itself is made up of the hest parts avail-

able including a Hammarlund condenser for tuning purposes. The parts are sturdily mounted on a metal base, which in turn is placed into a beautiful crackle finished metal cabinet to completely shield its entire contents.

A set of four plug -in coils is furnished with the receiver and cover from 14 to 200 meters.

Truly does this set earn the statement "Round the World Reception."

Set of batteries, $2.25

Set of R. C. A. licensed tubes, $2.50.

$995 WITH COILS

1S Ta4t METERS

15í9D 9010150 15070200 M TERS METERS METERS

NEW - POWERTONE - NEW 3 STAGE P. P. 250 AMPLIFIER

Q U A L I T Y

The Powertone Electric C. points with pride to its new complete line of amplifiers and public address systems. Their new outfits boast of better quality at a better price.

The three stage amplifier pictured above is the finest of its kind available. It consists of 1 -224. 1 -227, 2 -281 rectifying tubes and 2 -250 push pull power amplifying tubes which insure maximum power output. The amplifier is so built that it can be used very well with either phonograph or microphone input.

The output will permit the use of four or five dynamic speakers which can be placed over a large area and give pleasing results.

Each amplifier is supplied with a fuse to prevent shorts consequently saving burning out of tubes and power transformer which in turn save the consumer time and expense.

The amplifier comes complete with a built in volume control with which the operator can control The volume front a whisper to the highest volume of sound or speech.

PRICE

Complete net of R. C. A. licensed tubes. $7.50 2 4 L

5 TUBES

POWERTONE DIRECT

COUPLED AMPLIFIERS

JENSEN DYNAMIC SPEAKER CHASSIS

The tone and quality of these reproducers are unsurpassed. Will reproduce faithfully under the most trying conditions. These speaker outputs are available for all new type tubes as well as the old.

A.C. Types. D -7 Jr. Auditorium (as pictured) uses 280 rectifying tube in conjunction with 8 mfd. electrolytic condenser which insures minimum hum.

JENSEN- A.C.-D.8 Dry Rectifier A.C. -D.7 Jr. Audit. Tube Rectifier

Concert Jr. Tube Rect. D.9 -2500 Ohm D.C. Field D.7 -2500 Ohm D.C. Field D.15- Midget, 2500 Ohms.

$14.95 9.95 7.50 6.95 7.50 4.75

POWERTONE MIKE INPUT STAGE TI' r i

ßa7Si y .r held t I h' r

S I.

oorncy roman

tilri' i . diPito ns imMdnne, nnoaeon iComplete sielding avoids Imddi k.

t A handsomely finished Mack r, 1 ( e vale, orl Ì...a hour, ihr unit. `- - is

`rte: on the ..,, gat, r'dnn

- .1 with a to fiat adiustmen . Battery cum r men. -

bi-. tootle buolun. `ma For double button.

,w

Our Price $3.50 Our Prate $4.95

BANQUET MIKE STAND Extends from 1, to

30 inches. The ring will fit any standard size microphone. Due to a limited supply we advise you to get one at this low price. Price. $3.50

All the latest feature.; have been incorporated in the NEW powertone direct coupled amplifiers. A microphone can be utilized with the proper transformer and dry cell batteries for public address systems, no input, transformer is necessary for use with either radio set or phonograph for amplification purposes.

t Model 245 uses 1 -245. 1 -224 and 1 -280. Output is rated at $10.95 3 watts. Price less tubes Model 247 uses 1 -224. 1 -280 and 1 -247. Output is rated at 5512.95 2.5 watts. Price less tubes Model 250 uses 1 -224. 1 -281 and 1 -250. Output is rated at 5515.25 6 watts. l'rice less tubes

POWERTONE PORTABLE AMPLIFIER A ...slain and .rrinllr

trot a iplitir which tir ,pier public addre.,.retem i r..11 The case.

th a.

a ill, . t cuter. micropnnne

be tarried around to any dra;d"le Ï.. ¡'t,w. A .witch control in the rear ombles one to use a Phonna,.ph ni knp nr Mir a hone by

tappli.nctuú ,witch without any

The amplifier comes complete with tubes. 1 -224. 1 -24). and 1 --243. n R. C. A. microphone and C battery for usa with

PRICE Complete

All offers are F. O. B. New York, and subject to prior sale. Terms: A deposit of 20% is required with every order. Balance may be paid on delivery. Or, deduct 2% if full amount is sent with order. Mention catalog number when ordering.

GRENPARK CO., Dept. R. C.


245 GREENWICH STREET, NEW YORK, N. Y.

381



SEND NO MONEY--

Clip and mail to us coupon below. We will send you either one or both books through the Express Com- pany for your inspection. You have the privilege of

keeping or returning them.

If you want to have a complete set of all Radio Diagrams, both manuals should be in your file.

Official Radio Service

Manual

Volume II, 1932 Editi ,:

Both volumes of the OFFICIAL RADIO SERVICE MANUAL will give you the most complete set of circuit diagrams ever published for the Radio Industry. Every Radio Service Man and Dealer should have them available for immediate use in his business. Professional set -builders and amateurs will find them instructive and helpful.

Briefly outlined below are the "high spots" that are to be found in the 1931 Manual - the first complete radio service manual ever to be published. Over twenty -seven thousand copies of this edition were sold to members of the radio industry. This as- sures you of its importance to those engaged in radio and how valuable it is to them.

Partial Contents Wiring diagrams of radio sets manufactured since 1927, and many earlier ones of which there is no record elsewhere. 650 pages of radio -servicing material. Complete course of instruction for Radio Service Men, dealers, manufacturers, jobbers, set builders and amateurs. (Here are but a few of the subjects covered in the special course of instruction.) Amplifiers Antennae Automotive Condensers Detectors Eliminators Meters

Power -Supply Systems Radio Phonograph

Radio Equipment Resistors Short -Wave Sets Speakers Tubes

$4.50 Complete with Supplements

650 PAGES (Complete with Supplements)

Over 1,500 Diagrams, Charts and Illustrations

CLIP COUPON AND MAIL TODAY!

GERNSBACK PUBLICATIONS. Inc. Re -IS 96 -98 Park Place. New York, N. Y.

Please send me for FREE Inspert Ion. the hooks I have i herked below. 1 understand I may examine them carefully, und should I deride to keep them. I will pay the full cost. plus the few Vente for carrying charges. This offer Is good only in the U.S.A. [ ] Volume 1, 1931 Manual. with Supplement, $4.50. [ ] Volume II. 1932 Manual, with Supplements to be mailed Free

every 60 days. $5.00 [ ] BOTH BOOKS FOR $9.00.

Name

Address

City State

382

Flexible

Looseleaf

Binder,

9 x 12 inches.

Get Supplements FREE with the NEW 1932 MANUAL

There is so much new material in this Manual, that a Service Man or dealer would be lost without it when called to service a set. Information about new models which have been on the market only a few weeks are contained in this book. The 1932 Man- ual makes the service kit complete. The 1932 Manual contains a Full Radio Service Guide nd a Complete Directory of all 1931.1932 Radio Diagrams, also models of older design. Every- one in the Radio business should have a copy. Send for yours today!

Partial Contents of Volume II A step -by -step analysis in servicing a receiver which embodies in ifs design every possible combination of modern radio practice; it is fully illustrated and thoroughly explained. It is the greatest contribu- tion to the radio service field. Chart showing the operation of all types of vacuum tubes, whether new, old or obsolete. An exclusive resume of the uses of the Pentode and Variable -Mu Tubes and their characteristics. Complete discussion of the superheterodyne and its inherent peculiarities. Also a special chapter on tools used on superheterodyne circuits. Schematic diagrams and circuits complete with color codings. Important chapters on commercial aircraft radio equipment new data on commercial short -wave receivers and converters. Servicing and installation of public address systems and talking machine equipment. Standardized color- codings for resistors. Operation of old and new testing equipment; tube voltmeters, output meters, oscillators and aligning tools. A full section on Midget radios -their design, d r- cuits, and types. How to service them most eco- nomically. Hundreds of schematic diagrams of older radio receivers which have never been published. Blank pages for recording notes, diagrams and sketches; these pages are transferable to any part of the book. Coupon page for tree questions and answers.

$5.00 Complete with Supplements

OVER 1,000 PAGES (Including Supplements)

Over 2,000 Diagrams, Charts and Illustrations

Flexible, Looseleaf Binder, 9 x 12 inches.

NOT ONE OF THE DIAGRAMS PUBLISHED IN VOLUME

NUMBER I OF THE OFFICIAL RADIO SERVICE MANUAL

IS REPEATED IN VOLUME NUMBER II.




4 i

DECEMBER SPECIALS!! EVERY month we iist on this page certain STAR * items, which are

NOT LISTED IN OUR CATALOG. These are all specials of which the quantities on band are not sufficient to catalog them. Once sold out, no more can be had. First come, first served. ORDER NOW, TODAY.

STOP SHOPPING. The lowest prices are right on this page- No and undersells us. We meet any price on ANY NEW Merchandise. Order direct from this page and save money. 100% satisfaction on every transaction. Take advantage of these special offers. ORDER NOW, TODAY.

( ; - M PHOTO -RELAY SWITCH For 110 -20 Volts 60 Cycle A.C.

This new unit is an actual Photoelectric Relay containing a I l the principal parts used in the more costly indus- trial units. It comes fully equipped with a VISITRON Type B Cae- sium Cell. Magnetic Be-

lay With IMO' Mal winding a n ti silver contacte,

Transformer of large capacity. Amplifier Tube, Wire-Wound Potentiometer. Conden- sers. Terminal Strip, Sockets, Chassis. etc. This unit can be made the foundation of auch photoelectric applications ae burglar alarms, door -opening equipment, illumina- tion control, rare timing, counting. control of window disrtays and lllumhtation, and myriad other Installations. The Foto- Switch Ne. 1222A -Plate- Switch. $15.00

Your Price W

'114"

"MEGADYNE" ONE -TUBE PENTODE LOUDSPEAKER RECEIVER KIT

In the front part of our now -there is presented a 9100 on Ume construction

catalog -get your FREE copy thoroughly illustrated discus - and operation of the MEG'

ADYNE Receiver by Hugo Gems- back, editor. This ingenious circuit was originally described in t h e July issue of the RADIO C ILtFT Magazine, FREE copy of which will be given with each purchase. This receiver le indeed one of the most outstanding

developments In the radio Industry. It is the first real one -tube receiver which will actually operate a loudspeaker. Thousands of experimenters and radio fans will want to build this remarkable receiver. For their con - venlen e. we have compiled a complete list of parts required for its construction. These Pans are of the hiahest tlualit and are exactly as specified by the author. The follow ng pans comprise the complete kit.

* "PEERLESS" DIRECT COUPLED AMPLIFIERS

All the latest features in amplifier design have been ineorporated in this direct coupled amplifier. Input terminals for permitting phonograph attachment, and In addition, by attaching the proper microphone transformer, also dry cell batteries. a microphone may be used for public address work. Any type of receiver can be connected to the input terminals without fear of loss of energy. These amplifiers are for use with dynamic speakers. Amplifiers supply field current of 2500 ohm, to dynamic speakers. Resistors are furnished when A.C. speakers are used. Amplifiers operate on 110 volts, A. C., 60 cycles. Model SP5003 uses 1 -224. 1 -215 and 1 -250. Output is rated at 3 watts, Ne. SP 5003 -Your Price $10.95 (less tubes) Exactly the same amplifier, but employs a power pentodo in place of the 245 tube. Output 3.5 watts. No, SP 5004 -Your Prim $12.95 (less tubes) Model SP -5005 uses 1 -224, 1 -250 and 1 -281. Consumption is 85 watts; maximum undistorted output, 8 watts. Gain rated at 1000 cycles, 55áb; gain at 10,000 cycles, 51.5. Input direct to 2221 control grid; output direct from 250 plate. No. SP5005 -Your Pries $15.25 (lese tubes)

* SYNCHROMATIC ELECTRIC CLOCK

Never was such a first class electric clock sold at such ridiculously low price. An electric clock using the famous synchronistic move -

ant. Nasal observatory time right from your light socket! No spring to wind. no batteries. Never out of order. Lubricated for a life -time at the rectum.. Enclosed In a dust - proof and shockproof genuine molded Bakelite case. The case Is of walnut -brown finish with simple but catching design. For 110 volta, 60 cycle A.C. operation only, Complete with cord and attachment plug. Site 3% "x4!6 "xt%'. Weight 1 lb. Service men now sell these fine clocks by the

hundreds. Be We first In your locality to handle them.

List Pries $3.00 No. 1889-- Synchromatie Electric. Clock. $1.00

Your Price W

1 It.M.S. Fixed Crystal De- tector; 1 6.ollm Filament Rheostat; 1 3- circuit tuner for use with a .0005 nit tuning condenser: 1 Na aid type 481 UV 5 -prong socket: 1 Ilammarlund type ML -23 Variable Condenser; 2 sets of Cinch double binding poets; I Polymet .00025 mf. fixed condenser; 1 X -L Varloden- ser: 1 Pulymet .00025 mf. fixed condenser, or 1 Polymet .0005 mf. fixed condenser. (NOTE: Only one of the

latter two condensers is actually emphq'ed in the circuit)' 5 Fahnestocà binding posts" 1 25 -ft. roll of hookup Wire: 2 black Bakelite 1t4" knobs; 1 Kurs Kasch vernier dial with 0 to 100 grate reading clockwise: 1 type 38 pentode tube. "Triad" or "Speed" : 1 Bakelite Panel already drilled with all helm, size 7 x 10 x 3,16 Inch; 1

hardware assortment. The wooden base is not included.

No. 2545- MMadyne Receiver Kit. í1O.25 Your Price.... $

FREE RADIO AND SHORT WAVE TREATISE The new and enlarged Summer edition of our Radio and Short Wave Treatise, No. 25. has just come uff the press - 100 solid panes of useful Information. radio items. diagrams and Illustrations. Positively the greatest book in print - NOT JUST ANOTHER CATALOG. Con- tains a large editorial section with valuable information not found anywhere else. Considerable apace le devoted to a TREATISE ON SNORT WAVES for lath beginners and regular 'hums." Among the new technical information listed are the following: Modernizing old radio sets -repairing speakers and head sets -making superhets out of old sets - data on constructing twovolt battery and automobile receivers- eireult of the famous Gernsback Megadyne One -Tube Loudspeaker Set -short wave coil winding data -discussion on S.W. adapters. converters and receiver. etc., etc. WRITE TODAY. Enclose 4 cents for postage. Treatise sent by re-

turn mail. 100 New Hook -Ups, Etc.

1000 Illustrations.

* SILVER -MARSHALL AUDITORIUM AMPLIFIER

CONTAINS 2 STAGES SUPER POWER A. F. AMPLIFICATION

Ideal for theatres seating approximately 3.000 people. dance halls, schools lectures, hospitals, auditoriums, outdoor gatherings, etc., etc. The gigantle Power is at hhome as theavolumescanitbenres lated downllto a whisper!can

be used m an?

Supplies all nece>wary A, B and C. power to its own tubes, Operation requires ono type X230 power tube. one X226 A.C. tube and two type X281 rectifier tubes. Attractive crystalline Sitial, metal cabinet. 21x5%x5t4 in. Shipping aright. 38 Ills. No, SP- 5008 -Your Price $12.75 *METALLIZED PIGTAIL RESISTO A very fortunate purchase enables us to offer them fine resistors at prices which surprise even

u selves

prices more than three times lower than In our own rata - log. Resistors are guaranteed to maintain their ohm - ace under even adverse op. fit ng conditions The re-

sistance element Is based on the famous metallized prin- eipl whirls has proven Its No. SP2228. M superiority wherever arcur- Bred Resistors ary rid uniformity are para- YOUR moo t requisites. The attelal PRICE Ceramic rasing of these re- 12 for 60c.

RS AT ROCK BOTTOM PRICES sisters Is of sturdy construction and affords maximum heat dissipation. A feature of these resistors U their molded end -caps. tapered so they ran be mounted in all standard resistor mounts. By means of their pigtails. they may also be soldered to any convenient position. Availa- ble in the followingsizea -all rated at one watt: 300, 450,

stet- 000, 8,000, 10.000. 12.000. . NOW 350.000. Act fast to take

6t advantage of this offer, as the supply le limited. Sold

EACH only In lots of six or more.

Values Clearly Marked on Each

Unit

ELIMINATES NOISE AND CROSS -TALK

Service m e n throughout the world are beginning to realize the importance as well as the advantages obtained through the use of a shielded lead - in wire from antenna to radio receiver. More than 75 per cent of the complaints of "noisy" and

unselective receivers m a y be eliminated by merely replacing tito old, unshielded wire which leads from the aerial on the roof to the radio set with this new type of wire. Not only does it help to clear radio noises but to a certain extent, it makes the receiver more selective due to the capacity effect between the

w ire core and

the metal shield. Easily installed. The wire core is connected between aerial on the roof and antenna post on receiver. The outer shield is connected to ground. Every service man should carry at least one spare roll of shielded wire In his service kit. No, 1665. 50 Ft. Roll

Shielded Lead In Win.. Ns. 1668. 100 Ft. Roll 1.60 Shielded Lead -in Wire..

* PORTABLE PUBLIC ADDRESS SYSTEM

Comprises Micro- phone, Loftin -White Amplifier and Dyna wile Speaker. A recently Otist feted all - electric A.C. develop-

ment Incorporat- ing all the fee turee and advantages of the direct - coupled Loftin -White

Amplifier principle. The amplifier Is a high quality two st ace job, having some RADICALLY NEW IDEAS IN AUDIO FREQUENCY AMPLIFICA TION and employing 1 -'27, 1 -'45 power tube and 1 -'80 full -wave rectifier. It is remarkably free from A.C. hum.

The design is adaptable to all purposes. i.e., microphone. radio and Pho- nograph. Bas an undistorted power output of approximately 3.5 watts: SUFFICIENT TO OPERATE FROM 2 TO 3 ADDITIONAL DYNAMIC SPEAKERS.

The portable address system is sold COMPLETE WITH THE NEW R.C.A. VICTOR NAND MICROPHONE.

Put up in a single compact and per. featly balanced carrying case. the front of which Is utilized as a barre for the self -contained dynamic speaker. Com- plete with microphone and accessories the weight is only 30 pounds. For 50- 60 cycles, 110 -120 volts A.C. operation, Shipping weight. IS pounds.

List Price. $75.00 No. SP5011- Versatile Portable Address System Your Price. corn- $24.95 plate with microphone.., W

\r} * PRIME

"GREEN GIANT" Electric Phonograph Motor Induction type model with newly improved, humless motor. Equipped with speed regulator, also "ooh and off" switch. Completely equipped with large turn -table -takes records up to 12" in diameter. An Ideal motor for electri- fying the old phonograph. When used in conjunction with any amplifier um this page superb electrical repnsimai m Is out a feed. No. 100 -Your Price $7.50

WE ARE A WHOLESALE HOUSE AND CAN- NOT ACCEPT ORDERS FOR LESS THAN $3.00.

If C. O. D. shipment is desired. please remit 20% remittance, which must accompany all orders.

If full cash accompanies order, deduct 2% discount. Send money order -certified cheek -il. S. stamps.

Radio Trading Co. 23 West Broadway

New York, N. Y.

ORDER FROM THIS PAGE. You will find special prices from time to time in this magazine. Get our big FREE catalog for the it Radio Bargains.

Should you wish goods shipped by parcel poet. be sure to include sufficient extra remittance for same. Any excess will be refunded.




RADIO SERVICE MEN and DEALERS

here's the Catalog #.THAT HAS BECOME A

RADIO INSTITUTION!

933 WHOLESALE RADIO SERVICE CO..

100 SIXTH AVENUE NEW YORK

One of This Catalog's Many Features - LAFAYETTE perfected PUBLIC

ADDRESS SYSTEMS and AMPLIFIERS This year there has been more interest -and more business -in public address systems and amplifiers than ever before in the history of radio. Recognizing that fact we have listed in our new catalog the most advanced types of public address equipment and amplifiers. For example, the new LA- FAYETTE LOFTIN -WHITE "CLASS B" AMPLIFIER will drive 20 full size dynamic speakers. This is the first amplifier to combine the advantages of the Loftin -White principle with the tremendous power

gain of the recently developed "Class B" circuit. The new LAFAYETTE 250 PUBLIC ADDRESS SYS- TEM, with Loftin -White "250" Push -Pull Amplifier, is the most modern type equipment available today -at prices star- tlingly low.

Microphones-amplifiers-complete equipment of all kinds - everything the radio service man needs to increase his earn- ings in a rapidly growing field. Full details and descriptions in our catalog -write for it.

It started -just 11 years ago -as an Idivary mail order radio catalog. Undoubtedly you've seen the kind -there are lots of them around today. But the first crude catalog of 11 years ago had the same purpose behind it that today's magnificent WHOLE- SALE CATALOG has -to sell everything the radio service man and dealer needs at the lowest prices -to give him unexcelled service! Perhaps that is the reason why, after 11 years of phenomenal progress. the WHOLESALE RADIO SERVICE CATALOG is read by more people - serves more customers -has the largest and greatest circulation of any radio catalog ever issued. It has spread all over the world -its issuance is a

matter of interest to the radio industry at large - it has truly become a radio institution -a book that is responsible for more business than any piece of printed literature ever produced in radio. * 11 Years of Radio Reliability It goes without saying that the company behind such

an undertaking grew and kept pace with its offspring -became institutionalized in the same sense that its catalog did. For 11 years WHOLESALE RADIO SERVICE COMPANY has maintained a reputation as the "reliability house of radio." During business storms and business wars- prosperity booms and

depressions - fair competition - imitators by the scores -our business has grown -our facilities con-

stantly expanded -until today WHOLESALE RA- DIO SERVICE COMPANY is the largest institution of its kind in the world.

* Coupon Brings Catalog! Growth of this kind must have a powerful, vital force in back of it. No business can make such

tremendous strides unless it has a guiding policy that has met with the approval of its customers. You can discover these reasons for yourself -by examin- ing our catalog or by doing business with our com-

pany. The catalog will show you an 11 year old

policy -to sell the finest radio merchandise at the lowest WHOLESALE prices. Your very first transaction will illustrate our adherence to the slo-

gan-the fastest, quickest, most reliable service in all radio!

We suggest -mail the coupon below for your FREE catalog.

r WHOLESALE RADIO SERVICE CO., 100 Sixth Ave., Dept. G -55, New York, N. Y.

I shall be glad to receive a FREE copy of your new 1933 radio catalog. Please mail it immediately.

Name

Address

Town State

=M. i =No 4=10 =MI ID .ID MMI IM



RADIO -CRAFT FOR DECEMBER 384A

A Service Man's Proportional - scale Ohmmeter

FRANK ZOLTOWSKI

POST CARD PLACE

Ic

STAMP

HERE

WITH resistance values ranging commonly between 60 and 100,000 ohms, it becomes quite a problem to the Service Man to check up on them even if we quite neglect speed

and accuracy; his needs call for an ohmmeter of very wide range. However, the instrument should be fairly accurate, fast in operation, small in size and of low cost.

After much figuring and doping the writer came to the conclusion that the only way to secure a sufficiently wide range of resistance measurements with the apparatus available was by using the voltmeter and ammeter method. By this system of connections, Fig. 1A, it is possible to find the value of an unknown resistance by dividing the applied voltage by the observed current.

Following a number of measurements with this set -up, the thought arose that it would be nice to have a smooth, variable source of applied voltage, so that the voltage could be adjusted until the current was an easy decimal quantity. For instance, we take an unknown resistance and connect it in position as in Fig. 1B, and by means of the variable voltage divider, the potentiometer, we adjust the voltage until the milliammeter reads .001 -A. Now we observe on the voltmeter the amount of voltage required to pass .001 -A, through the resistor; in this case, we will say, it is two volts, therefore.

R° Ì or 2 +.001 =2,000 ohms. Easy? You do not have to do it on paper, just simply read the

voltage and then in your mind point off three places. To divide by .001 is the same as multiplying by 1,000 and to multiply by 1,000, point off three places to the right. Thus, to find the value of an unknown resistance, just connect in the "unknown," adjust Lincoln Radio Corporation the voltage, multiply by 1,000, and there is your answer in ohms.

Now think a minute -if we are going to keep our current at .001 -A., when making a measurement, then it is going to take 1 V. to push it through 1,000 ohms, 2 V. for 2,000 ohms, 8 V. for 3,000 ohms, and so on up the scale. Now if that is the case you are getting your ohm readings direct from the scale of the voltmeter (times 1,000) and that is a straight -line scale -something out of the ordinary for ohmmeters.

So far we have done pretty well and we have about decided that the ammeter in this arrangement will have a full -scale value of 1. ma. If it takes 1 V. per thousand ohms to operate the meter then it will require 100 V. to reach our high ideal of 100,000 ohms.

A battery of this rating would constitute too much bulk and weight. Let us decide that three of the regular 4.5 V. "C" battery units are all that we can carry or conveniently put in the case; this will give us a maximum of 13.5 V. and if we allow for "wear" we should always be able to obtain 10 V. from them. We will use a voltmeter with a range of 10 V. (any internal resistance) to read the voltage impressed on the unknown resistance.

Although it seems that our range in measuring ohms will be POST CARD limited to 10,000, this need not necessarily be the case, because there is another way out. Instead of adjusting the voltage until the milliammeter reads .001 -A., just adjust it to one -tenth of the scale or .0001 -A., then multiply the reading of the voltmeter scale by 10.000 instead of 1.000. This means that if .0001 -A. is flowing at a voltage of 10 then the resistance in the circuit has a value of 100,000 ohms.

Perhaps you are beginning to see now that the ammeter serves principally as a multiplying indicator telling you by how much to multiply the volt scale in order to read directly the ohms in the circuit.

We have found how to get two ranges with the instrument: 0 Newark to 10,000 by using a multiplying factor of 1,000 and: 0 to 100.000 by using a multiplying factor of 10,000. We can extend this multiplying scheme a little more and get an advantage in widening the range between 0 and 1,000 ohms so as to make it more readable. This L ae. compliehed by placing a multiplying shunt on the milliammeter so as to give it a range of 10 ma.. or .01 -A. With the shunt switched in we adjust the multiplying indicator to full -scale and multiply the reading on the "volt" scale by 100. We will thus be able to read clearly from 50 to 1.000 ohms.

A circuit of the completed instrument is shown in Fig. 1C. A switch is provided to cut off the 400 ohm voltage divider so that it will not bleed the batteries when not in use. The pilot light P. L. is a further precaution against leaving the switch in the "on" position when the instrument is not in use. The better the meters used. of course, the greater will be the accuracy. A suggested arrangement of the nppar- tua is shown in Fig. 1D.

Dept. G55

100 Sixth Avenue

NEW YORK, N. Y.

R o- 1.MA

IOMA. SHUNT

0-10 v o IlI *Id+. A-

R

411)

Illikr". 151/21t

4 101111 o-RI8I1I1Ia

S MILLIAMMETlR ' i ! VOLT METEit

MIN1Por MNi)

1,1,07 LAMP

ON OFF.K: . 10 MA SMVNT.?R.++.^'`4.

. 1..á

F

rl

Fig. 1. Ohasater circuita; Iliad layout.

POST CARD PLACE

le

STAMP

HERE

Dept. RC -12

329 South Wood Street

CHICAGO, ILLINOIS

PLACE

Ic

STAMP

H ERE

Electric Company

226 West Madison Street

CHICAGO, ILLINOIS

POST CARD

Cable Radio Tube Corp.

230 -242 North 9th Street

Br")OKLYN, NEW YORK

i



December RADIO -CRAFT Wholetele Radio Service Co., Int., 100 Sixth Avenue, New York, N. Y.

Attention: Dept. 055

I obeli be glad to receive FREF. ropy of gour NEW 1933 Radio Catalog. Kindly mall It Im- medtatel7.

Name

Addreat

Town and State _

December RADIO -CRAFT Lincoln Radio Corporation

Dept. RC-12, 329 South Wood Street

Chicago, Illinois

Please send me information on ( ) A. C. ( ) D. C. receivers

Name

Address

City State

Newark Electric Company

226 West Madison Street

Chicago, Illinois

Please send me information about TOBE FILTERIZERS.

N.1me

Address

December RADIO -CRAFT

City State

December RADIO -CRAFT Cable Radio Tube Corp. 230 -242 North 9th Street Brooklyn, New York

Gentlemen: Please send me current bulletins without charge or obligation on the items checked:

( ) SPEED Radio Tubes ( ) SPEED Television Tubes li SPEED Foto -Lectric Tubes

SPEED Triple -Twin Group

Name

Address

Ilk State

RADIO -CRAFT FOR DECEMBER 384B

How to Get "Java" With a Simple P. A. System

PAUL RICHARDS MODERMODERN ingenuity has solved the problem of serving N

greater number of customers than ever before, in the Loft candy store at 251 W. 42nd SL, New York

City, through the use of a public address system of very simple design, as shown in Fig. A. Service Men will do well to take the tip -store owners everywhere are willing to consider any reasonable proposition which will enable them, without exorbitant expense, to secure increased return from the same floor space.

Pretty waitresses tend a counter devoid of everything but water spigots, as shown in the upper portion of Fig. A; soda fountains, drink mixers, ice cream tanks, coffee urns, and the short -order counter, attended by clerks, all are located in the basement, as shown in the lower portion of the view.

As the customer gives the order, the waitress repeats it into one of six Universal. type X chrome -plated two -button microphones, which are mounted in Universal type Banquet chrome - plated microphone stands; two of these appear in Fig. A. Micro- phone current is obtained from equipment in the basement; an "off-on" button is provided at each microphone stand and must be operated whenever an order is to be given.

The output of each pair of microphones terminates in the basement at special amplifier- reproducer cabinets. These three units appear in the lower portion of Fig. A; each instrument is permanently connected to a 110 V., A.C. outlet. Within each cabinet are contained a Wright -DeCoster dynamic reproducer; a Universal type 1089 two -button microphone transformer, and; an Electrad type B -250 Loftin -White direct coupled amplifier. The schematic circuit of the latter unit is Fig. 1.

The power consumption of this amplifier is 85 W.; the maximum undistorted power output, 4.6 W. Additional specifications are as follows: Gain at 100 cycles, 52.5 db.; 1000 cycles, 55 db.; 10,000 cycles, 51.5 db. Input potential for maximum output, 0.28 -V.; hum level, 0.4 -V.

A high -speed dumbwaiter alongside each clerk promptly carries the completed order to the floor above.

Thus, modern magic has opened for the technician one more lucrative field. Every store owner who feels that the street - level floor space for which he pays a high rental is not adequate to meet his needs, will do well to consider the possibility of adapting available low- rental space above or below, through the use of a simple public address system.

Y

Fig. A, above. In the upper portion

of this view are shown microphones into which pretty waitresses in a Loft store in New York City pass to the room below the order for "Java and - " The amplifier - reproducer cabinets in the room below appear in the lower section of the figure.

Fig. 1, right. Schematic circuit of

the Electrad type B -250 direct -coupled "L -W" type amplifier contained in the ca i-

'24 'so

npOT

2MP LN.

CT



Documents

RADIO'S LIVEST MAGAZINE...500 S. Paulina St., Dept.92.8H Chicago, Ill. Dear Mr. Lewis: Send me your Big. FREE Radio Book. and tell me how f can get the TRAINING that will make me a